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class="w-full pt-6 scrolling-touch lg:h-auto grow pe-0 lg:pe-5 lg:pb-16 md:pt-4 lg:pt-4 scrolling-gpu"><ul><h3 class="mb-1 text-sm font-bold ms-5 text-tertiary dark:text-tertiary-dark">GET STARTED</h3><li><a title="Quick Start" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between ps-5 text-base font-bold text-primary dark:text-primary-dark" href="/learn"><div>Quick Start </div><span class="pe-1 text-tertiary dark:text-tertiary-dark"><svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" class="duration-100 ease-in transition -rotate-90 rtl:rotate-90" style="min-width:20px;min-height:20px"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg></span></a><div class="opacity-50" style="transition:opacity 250ms ease-in-out"><div id="react-collapsed-panel-:R8im6:" aria-hidden="true" role="region" style="box-sizing:border-box;display:none;height:0px;overflow:hidden"><ul><li><a title="Tutorial: Tic-Tac-Toe" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/tutorial-tic-tac-toe"><div>Tutorial: Tic-Tac-Toe </div></a></li><li><a title="Thinking in React" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/thinking-in-react"><div>Thinking in React </div></a></li></ul></div></div></li><li><a title="Installation" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between ps-5 text-base font-bold text-primary dark:text-primary-dark" href="/learn/installation"><div>Installation </div><span class="pe-1 text-tertiary dark:text-tertiary-dark"><svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" class="duration-100 ease-in transition -rotate-90 rtl:rotate-90" style="min-width:20px;min-height:20px"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg></span></a><div class="opacity-50" style="transition:opacity 250ms ease-in-out"><div id="react-collapsed-panel-:R8qm6:" aria-hidden="true" role="region" style="box-sizing:border-box;display:none;height:0px;overflow:hidden"><ul><li><a title="Start a New React Project" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/start-a-new-react-project"><div>Start a New React Project </div></a></li><li><a title="Add React to an Existing Project" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/add-react-to-an-existing-project"><div>Add React to an Existing Project </div></a></li><li><a title="Editor Setup" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/editor-setup"><div>Editor Setup </div></a></li><li><a title="Using TypeScript" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/typescript"><div>Using TypeScript </div></a></li><li><a title="React Developer Tools" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/react-developer-tools"><div>React Developer Tools </div></a></li><li><a title="React Compiler" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/react-compiler"><div>React Compiler <svg class="ms-2 text-gray-30 dark:text-gray-60 inline-block w-4 h-4 align-[-3px]" width="20px" height="20px" viewBox="0 0 20 20" version="1.1" xmlns="http://www.w3.org/2000/svg"><title> - This feature is available in the 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id="Shape"></path></g></g></svg></div></a></li></ul></div></div></li><li role="separator" class="mt-4 mb-2 ms-5 border-b border-border dark:border-border-dark"></li><h3 class="mb-1 text-sm font-bold ms-5 text-tertiary dark:text-tertiary-dark mt-2">LEARN REACT</h3><li><a title="Describing the UI" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between ps-5 text-base font-bold text-primary dark:text-primary-dark" href="/learn/describing-the-ui"><div>Describing the UI </div><span class="pe-1 text-tertiary dark:text-tertiary-dark"><svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" class="duration-100 ease-in transition -rotate-90 rtl:rotate-90" style="min-width:20px;min-height:20px"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg></span></a><div class="opacity-50" style="transition:opacity 250ms ease-in-out"><div id="react-collapsed-panel-:R9am6:" aria-hidden="true" role="region" style="box-sizing:border-box;display:none;height:0px;overflow:hidden"><ul><li><a title="Your First Component" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/your-first-component"><div>Your First Component </div></a></li><li><a title="Importing and Exporting Components" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/importing-and-exporting-components"><div>Importing and Exporting Components </div></a></li><li><a title="Writing Markup with JSX" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/writing-markup-with-jsx"><div>Writing Markup with JSX </div></a></li><li><a title="JavaScript in JSX with Curly Braces" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/javascript-in-jsx-with-curly-braces"><div>JavaScript in JSX with Curly Braces </div></a></li><li><a title="Passing Props to a Component" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/passing-props-to-a-component"><div>Passing Props to a Component </div></a></li><li><a title="Conditional Rendering" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/conditional-rendering"><div>Conditional Rendering </div></a></li><li><a title="Rendering Lists" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/rendering-lists"><div>Rendering Lists </div></a></li><li><a title="Keeping Components Pure" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/keeping-components-pure"><div>Keeping Components Pure </div></a></li><li><a title="Your UI as a Tree" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/understanding-your-ui-as-a-tree"><div>Your UI as a Tree </div></a></li></ul></div></div></li><li><a title="Adding Interactivity" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between ps-5 text-base font-bold text-primary dark:text-primary-dark" href="/learn/adding-interactivity"><div>Adding Interactivity </div><span class="pe-1 text-tertiary dark:text-tertiary-dark"><svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" class="duration-100 ease-in transition -rotate-90 rtl:rotate-90" style="min-width:20px;min-height:20px"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg></span></a><div class="opacity-50" style="transition:opacity 250ms ease-in-out"><div id="react-collapsed-panel-:R9im6:" aria-hidden="true" role="region" style="box-sizing:border-box;display:none;height:0px;overflow:hidden"><ul><li><a title="Responding to Events" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/responding-to-events"><div>Responding to Events </div></a></li><li><a title="State: A Component's Memory" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/state-a-components-memory"><div>State: A Component's Memory </div></a></li><li><a title="Render and Commit" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/render-and-commit"><div>Render and Commit </div></a></li><li><a title="State as a Snapshot" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/state-as-a-snapshot"><div>State as a Snapshot </div></a></li><li><a title="Queueing a Series of State Updates" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/queueing-a-series-of-state-updates"><div>Queueing a Series of State Updates </div></a></li><li><a title="Updating Objects in State" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/updating-objects-in-state"><div>Updating Objects in State </div></a></li><li><a title="Updating Arrays in State" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/updating-arrays-in-state"><div>Updating Arrays in State </div></a></li></ul></div></div></li><li><a title="Managing State" target="" aria-current="page" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between ps-5 text-base font-bold text-base text-link dark:text-link-dark bg-highlight dark:bg-highlight-dark border-blue-40 hover:bg-highlight hover:text-link dark:hover:bg-highlight-dark dark:hover:text-link-dark" href="/learn/managing-state"><div>Managing State </div><span class="pe-1 text-link dark:text-link-dark"><svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" class="duration-100 ease-in transition rotate-0" style="min-width:20px;min-height:20px"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg></span></a><div class="opacity-100" style="transition:opacity 250ms ease-in-out"><div id="react-collapsed-panel-:R9qm6:" aria-hidden="false" role="region" style="box-sizing:border-box"><ul><li><a title="Reacting to Input with State" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/reacting-to-input-with-state"><div>Reacting to Input with State </div></a></li><li><a title="Choosing the State Structure" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/choosing-the-state-structure"><div>Choosing the State Structure </div></a></li><li><a title="Sharing State Between Components" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/sharing-state-between-components"><div>Sharing State Between Components </div></a></li><li><a title="Preserving and Resetting State" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/preserving-and-resetting-state"><div>Preserving and Resetting State </div></a></li><li><a title="Extracting State Logic into a Reducer" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/extracting-state-logic-into-a-reducer"><div>Extracting State Logic into a Reducer </div></a></li><li><a title="Passing Data Deeply with Context" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/passing-data-deeply-with-context"><div>Passing Data Deeply with Context </div></a></li><li><a title="Scaling Up with Reducer and Context" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/scaling-up-with-reducer-and-context"><div>Scaling Up with Reducer and Context </div></a></li></ul></div></div></li><li><a title="Escape Hatches" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between ps-5 text-base font-bold text-primary dark:text-primary-dark" href="/learn/escape-hatches"><div>Escape Hatches </div><span class="pe-1 text-tertiary dark:text-tertiary-dark"><svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" class="duration-100 ease-in transition -rotate-90 rtl:rotate-90" style="min-width:20px;min-height:20px"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg></span></a><div class="opacity-50" style="transition:opacity 250ms ease-in-out"><div id="react-collapsed-panel-:Ra2m6:" aria-hidden="true" role="region" style="box-sizing:border-box;display:none;height:0px;overflow:hidden"><ul><li><a title="Referencing Values with Refs" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/referencing-values-with-refs"><div>Referencing Values with Refs </div></a></li><li><a title="Manipulating the DOM with Refs" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/manipulating-the-dom-with-refs"><div>Manipulating the DOM with Refs </div></a></li><li><a title="Synchronizing with Effects" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/synchronizing-with-effects"><div>Synchronizing with Effects </div></a></li><li><a title="You Might Not Need an Effect" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/you-might-not-need-an-effect"><div>You Might Not Need an Effect </div></a></li><li><a title="Lifecycle of Reactive Effects" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/lifecycle-of-reactive-effects"><div>Lifecycle of Reactive Effects </div></a></li><li><a title="Separating Events from Effects" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/separating-events-from-effects"><div>Separating Events from Effects </div></a></li><li><a title="Removing Effect Dependencies" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/removing-effect-dependencies"><div>Removing Effect Dependencies </div></a></li><li><a title="Reusing Logic with Custom Hooks" target="" class="p-2 pe-2 w-full rounded-none lg:rounded-e-2xl text-start hover:bg-gray-5 dark:hover:bg-gray-80 relative flex items-center justify-between text-sm ps-6 ps-5 text-base text-secondary dark:text-secondary-dark" href="/learn/reusing-logic-with-custom-hooks"><div>Reusing Logic with Custom Hooks </div></a></li></ul></div></div></li></ul><div class="h-20"></div></nav><div class="fixed bottom-0 hidden lg:block"><div class="max-w-custom-xs w-80 lg:w-auto py-3 shadow-lg rounded-lg m-4 bg-wash dark:bg-gray-95 px-4 flex"><p class="w-full text-lg font-bold text-primary dark:text-primary-dark me-4">Is this page useful?</p><button aria-label="Yes" class="px-3 rounded-lg bg-secondary-button dark:bg-secondary-button-dark text-primary dark:text-primary-dark me-2"><svg width="16" height="18" viewBox="0 0 16 18" fill="none" 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9.42608C8.28237 9.42608 8.54595 9.5701 8.70195 9.80961C8.85794 10.0491 8.88558 10.3523 8.77555 10.6169L7.11114 14.6201C7 14.8875 6.98105 15.1852 7.05738 15.4649C7.1337 15.7446 7.30079 15.9897 7.53147 16.1605L7.62458 16.2294Z" fill="currentColor"></path></svg></button></div></div></aside></div></div></div></div><main class="min-w-0 isolate"><article class="font-normal break-words text-primary dark:text-primary-dark"><div class="ps-0"><div class=""><div class="px-5 sm:px-12 pt-3.5"><div class="max-w-4xl ms-0 2xl:mx-auto"><div class="flex flex-wrap"><div class="flex mb-3 mt-0.5 items-center"><a class="text-link dark:text-link-dark text-sm tracking-wide font-bold uppercase me-1 hover:underline" href="/learn">Learn React</a><span class="inline-block me-1 text-link dark:text-link-dark text-lg rtl:rotate-180"><svg width="20" height="20" viewBox="0 0 20 20" fill="none" xmlns="http://www.w3.org/2000/svg"><path d="M6.86612 13.6161C6.37796 14.1043 6.37796 14.8957 6.86612 15.3839C7.35427 15.872 8.14572 15.872 8.63388 15.3839L13.1339 10.8839C13.622 10.3957 13.622 9.60428 13.1339 9.11612L8.63388 4.61612C8.14572 4.12797 7.35427 4.12797 6.86612 4.61612C6.37796 5.10428 6.37796 5.89573 6.86612 6.38388L10.4822 10L6.86612 13.6161Z" fill="currentColor"></path></svg></span></div></div><h1 class="mdx-heading mt-0 text-primary dark:text-primary-dark -mx-.5 break-words text-5xl font-display font-bold leading-tight">Managing State<a href="#undefined" aria-label="Link for this heading" title="Link for this heading" class="mdx-header-anchor hidden"><svg width="1em" height="1em" viewBox="0 0 13 13" xmlns="http://www.w3.org/2000/svg" class="text-gray-70 ms-2 h-5 w-5"><g fill="currentColor" fill-rule="evenodd"><path d="M7.778 7.975a2.5 2.5 0 0 0 .347-3.837L6.017 2.03a2.498 2.498 0 0 0-3.542-.007 2.5 2.5 0 0 0 .006 3.543l1.153 1.15c.07-.29.154-.563.25-.773.036-.077.084-.16.14-.25L3.18 4.85a1.496 1.496 0 0 1 .002-2.12 1.496 1.496 0 0 1 2.12 0l2.124 2.123a1.496 1.496 0 0 1-.333 2.37c.16.246.42.504.685.752z"></path><path d="M5.657 4.557a2.5 2.5 0 0 0-.347 3.837l2.108 2.108a2.498 2.498 0 0 0 3.542.007 2.5 2.5 0 0 0-.006-3.543L9.802 5.815c-.07.29-.154.565-.25.774-.036.076-.084.16-.14.25l.842.84c.585.587.59 1.532 0 2.122-.587.585-1.532.59-2.12 0L6.008 7.68a1.496 1.496 0 0 1 .332-2.372c-.16-.245-.42-.503-.685-.75z"></path></g></svg></a></h1><div class="mt-4"><span class="me-2"><span class="inline font-bold text-sm uppercase py-1 px-2 rounded bg-purple-40 text-white">Intermediate</span></span></div></div></div></div><div class="px-5 sm:px-12"><div class="max-w-7xl mx-auto"><div class="max-w-4xl ms-0 2xl:mx-auto"><div class="font-display text-xl text-primary dark:text-primary-dark leading-relaxed"><p class="whitespace-pre-wrap my-4">As your application grows, it helps to be more intentional about how your state is organized and how the data flows between your components. Redundant or duplicate state is a common source of bugs. In this chapter, you’ll learn how to structure your state well, how to keep your state update logic maintainable, and how to share state between distant components.</p></div> <div class="p-6 xl:p-8 pb-4 xl:pb-6 bg-card dark:bg-card-dark rounded-2xl shadow-inner-border dark:shadow-inner-border-dark text-base text-secondary dark:text-secondary-dark my-8"><h3 class="mdx-heading text-primary dark:text-primary-dark mt-0 mb-3 leading-tight text-2xl font-display leading-9 text-primary dark:text-primary-dark font-bold my-6">In this chapter</h3><ul class="ms-6 my-3 list-disc"> <li class="leading-relaxed mb-1"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/reacting-to-input-with-state">How to think about UI changes as state changes</a></li> <li class="leading-relaxed mb-1"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/choosing-the-state-structure">How to structure state well</a></li> <li class="leading-relaxed mb-1"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/sharing-state-between-components">How to “lift state up” to share it between components</a></li> <li class="leading-relaxed mb-1"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/preserving-and-resetting-state">How to control whether the state gets preserved or reset</a></li> <li class="leading-relaxed mb-1"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/extracting-state-logic-into-a-reducer">How to consolidate complex state logic in a function</a></li> <li class="leading-relaxed mb-1"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/passing-data-deeply-with-context">How to pass information without “prop drilling”</a></li> <li class="leading-relaxed mb-1"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/scaling-up-with-reducer-and-context">How to scale state management as your app grows</a></li> </ul></div> <h2 id="reacting-to-input-with-state" class="mdx-heading text-3xl font-display leading-10 text-primary dark:text-primary-dark font-bold my-6">Reacting to input with state <a href="#reacting-to-input-with-state" aria-label="Link for Reacting to input with state " title="Link for Reacting to input with state " class="mdx-header-anchor inline-block"><svg width="1em" height="1em" viewBox="0 0 13 13" xmlns="http://www.w3.org/2000/svg" class="text-gray-70 ms-2 h-5 w-5"><g fill="currentColor" fill-rule="evenodd"><path d="M7.778 7.975a2.5 2.5 0 0 0 .347-3.837L6.017 2.03a2.498 2.498 0 0 0-3.542-.007 2.5 2.5 0 0 0 .006 3.543l1.153 1.15c.07-.29.154-.563.25-.773.036-.077.084-.16.14-.25L3.18 4.85a1.496 1.496 0 0 1 .002-2.12 1.496 1.496 0 0 1 2.12 0l2.124 2.123a1.496 1.496 0 0 1-.333 2.37c.16.246.42.504.685.752z"></path><path d="M5.657 4.557a2.5 2.5 0 0 0-.347 3.837l2.108 2.108a2.498 2.498 0 0 0 3.542.007 2.5 2.5 0 0 0-.006-3.543L9.802 5.815c-.07.29-.154.565-.25.774-.036.076-.084.16-.14.25l.842.84c.585.587.59 1.532 0 2.122-.587.585-1.532.59-2.12 0L6.008 7.68a1.496 1.496 0 0 1 .332-2.372c-.16-.245-.42-.503-.685-.75z"></path></g></svg></a></h2> <p class="whitespace-pre-wrap my-4">With React, you won’t modify the UI from code directly. For example, you won’t write commands like “disable the button”, “enable the button”, “show the success message”, etc. Instead, you will describe the UI you want to see for the different visual states of your component (“initial state”, “typing state”, “success state”), and then trigger the state changes in response to user input. This is similar to how designers think about UI.</p> <p class="whitespace-pre-wrap my-4">Here is a quiz form built using React. Note how it uses the <code dir="ltr" class="inline text-code text-secondary dark:text-secondary-dark px-1 rounded-md no-underline bg-gray-30 bg-opacity-10 py-px">status</code> state variable to determine whether to enable or disable the submit button, and whether to show the success message instead.</p> </div><div class="sandpack sandpack--playground w-full my-8" dir="ltr"><div class="sp-wrapper"><div class="shadow-lg dark:shadow-lg-dark rounded-lg" style="contain:content"><div class="bg-wash dark:bg-card-dark flex justify-between items-center relative z-10 border-b border-border dark:border-border-dark rounded-t-lg text-lg"><div class="flex-1 grow min-w-0 px-4 lg:px-6"><div><div class="relative overflow-hidden"><div class="w-[fit-content] invisible"><div class=" sp-tabs" translate="no"><div aria-label="Select active file" class=" sp-tabs-scrollable-container" role="tablist"><button aria-selected="true" class=" sp-tab-button" data-active="true" role="tab" title="/src/App.js" 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aria-autocomplete="list" aria-label="Code Editor for App.js" aria-multiline="true" class="sp-pristine sp-javascript sp-cm" role="textbox" tabindex="0" translate="no"><pre class=" sp-pre-placeholder" style="margin-left:var(--sp-space-11)"><span class="sp-syntax-keyword">import</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-plain">useState</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'react'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">export</span> <span class="sp-syntax-keyword">default</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">Form</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">answer</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">setAnswer</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useState</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">''</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">error</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">setError</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useState</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-keyword">null</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">status</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">setStatus</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useState</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">'typing'</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">if</span> <span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">status</span> === <span class="sp-syntax-string">'success'</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">h1</span><span class="sp-syntax-punctuation">></span>That's right!<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">h1</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">async</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">handleSubmit</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-plain">e</span>.<span class="sp-syntax-property">preventDefault</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-definition">setStatus</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">'submitting'</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">try</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">await</span> <span class="sp-syntax-definition">submitForm</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">answer</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-definition">setStatus</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">'success'</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">catch</span> <span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">err</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">setStatus</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">'typing'</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-definition">setError</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">err</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">handleTextareaChange</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">setAnswer</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span>.<span class="sp-syntax-property">target</span>.<span class="sp-syntax-property">value</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">h2</span><span class="sp-syntax-punctuation">></span>City quiz<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">h2</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">p</span><span class="sp-syntax-punctuation">></span> In which city is there a billboard that turns air into drinkable water? <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">p</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">form</span> <span class="sp-syntax-property">onSubmit</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">handleSubmit</span><span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">textarea</span> <span class="sp-syntax-property">value</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">answer</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">onChange</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">handleTextareaChange</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">disabled</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">status</span> === <span class="sp-syntax-string">'submitting'</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">br</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">button</span> <span class="sp-syntax-property">disabled</span>=<span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-plain">answer</span>.<span class="sp-syntax-property">length</span> === <span class="sp-syntax-static">0</span> || <span class="sp-syntax-plain">status</span> === <span class="sp-syntax-string">'submitting'</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">></span> Submit <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">button</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">error</span> !== <span class="sp-syntax-keyword">null</span> && <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">p</span> <span class="sp-syntax-property">className</span>=<span class="sp-syntax-string">"Error"</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">error</span>.<span class="sp-syntax-property">message</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">p</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">form</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">submitForm</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">answer</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-comment">// Pretend it's hitting the network.</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-keyword">new</span> <span class="sp-syntax-plain">Promise</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">resolve</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">reject</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">=></span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">setTimeout</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">=></span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">let</span> <span class="sp-syntax-plain">shouldError</span> = <span class="sp-syntax-plain">answer</span>.<span class="sp-syntax-property">toLowerCase</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> !== <span class="sp-syntax-string">'lima'</span> <span class="sp-syntax-keyword">if</span> <span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">shouldError</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">reject</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-keyword">new</span> <span class="sp-syntax-plain">Error</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">'Good guess but a wrong answer. Try again!'</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">else</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">resolve</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-static">1500</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> </pre></div></div></div><div class=" order-last xl:order-2 sp-stack"><div class="p-0 sm:p-2 md:p-4 lg:p-8 bg-card dark:bg-wash-dark h-full relative md:rounded-b-lg lg:rounded-b-none"><div style="position:relative"><iframe class="rounded-t-none bg-white md:shadow-md sm:rounded-lg w-full max-w-full transition-opacity absolute opacity-0 pointer-events-none duration-75" title="Sandbox Preview" style="height:15px;z-index:-1"></iframe></div></div></div><button translate="yes" class="sandpack-expand flex text-base justify-between dark:border-card-dark bg-wash dark:bg-card-dark items-center z-10 p-1 w-full order-2 xl:order-last border-b-1 relative top-0"><span class="flex p-2 focus:outline-none text-primary dark:text-primary-dark leading-[20px]"><svg class="rotate-0 inline me-1.5 text-xl" xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg>Show more</span></button></div></div></div></div><div class="max-w-4xl ms-0 2xl:mx-auto"> <section class="p-8 mt-16 mb-16 flex flex-row shadow-inner-border dark:shadow-inner-border-dark justify-between items-center bg-card dark:bg-card-dark rounded-2xl"><div class="flex-col"><h2 class="text-primary font-display dark:text-primary-dark font-bold text-2xl leading-tight">Ready to learn this topic?</h2><p class="whitespace-pre-wrap my-4">Read <strong class="font-bold"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/reacting-to-input-with-state">Reacting to Input with State</a></strong> to learn how to approach interactions with a state-driven mindset.</p><a class="mt-1 active:scale-[.98] transition-transform inline-flex font-bold items-center outline-none focus:outline-none focus-visible:outline focus-visible:outline-link focus:outline-offset-2 focus-visible:dark:focus:outline-link-dark leading-snug bg-link text-white dark:bg-brand-dark dark:text-secondary hover:bg-opacity-80 text-base rounded-full px-4 py-2" aria-label="Read More" target="_self" href="/learn/reacting-to-input-with-state">Read More<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" class="duration-100 ease-in transition -rotate-90 rtl:rotate-90 inline ms-1" style="min-width:20px;min-height:20px"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg></a></div></section><hr class="border-border dark:border-border-dark mb-14"/> <h2 id="choosing-the-state-structure" class="mdx-heading text-3xl font-display leading-10 text-primary dark:text-primary-dark font-bold my-6">Choosing the state structure <a href="#choosing-the-state-structure" aria-label="Link for Choosing the state structure " title="Link for Choosing the state structure " class="mdx-header-anchor inline-block"><svg width="1em" height="1em" viewBox="0 0 13 13" xmlns="http://www.w3.org/2000/svg" class="text-gray-70 ms-2 h-5 w-5"><g fill="currentColor" fill-rule="evenodd"><path d="M7.778 7.975a2.5 2.5 0 0 0 .347-3.837L6.017 2.03a2.498 2.498 0 0 0-3.542-.007 2.5 2.5 0 0 0 .006 3.543l1.153 1.15c.07-.29.154-.563.25-.773.036-.077.084-.16.14-.25L3.18 4.85a1.496 1.496 0 0 1 .002-2.12 1.496 1.496 0 0 1 2.12 0l2.124 2.123a1.496 1.496 0 0 1-.333 2.37c.16.246.42.504.685.752z"></path><path d="M5.657 4.557a2.5 2.5 0 0 0-.347 3.837l2.108 2.108a2.498 2.498 0 0 0 3.542.007 2.5 2.5 0 0 0-.006-3.543L9.802 5.815c-.07.29-.154.565-.25.774-.036.076-.084.16-.14.25l.842.84c.585.587.59 1.532 0 2.122-.587.585-1.532.59-2.12 0L6.008 7.68a1.496 1.496 0 0 1 .332-2.372c-.16-.245-.42-.503-.685-.75z"></path></g></svg></a></h2> <p class="whitespace-pre-wrap my-4">Structuring state well can make a difference between a component that is pleasant to modify and debug, and one that is a constant source of bugs. The most important principle is that state shouldn’t contain redundant or duplicated information. If there’s unnecessary state, it’s easy to forget to update it, and introduce bugs!</p> <p class="whitespace-pre-wrap my-4">For example, this form has a <strong class="font-bold">redundant</strong> <code dir="ltr" class="inline text-code text-secondary dark:text-secondary-dark px-1 rounded-md no-underline bg-gray-30 bg-opacity-10 py-px">fullName</code> state variable:</p> </div><div class="sandpack sandpack--playground w-full my-8" dir="ltr"><div class="sp-wrapper"><div class="shadow-lg dark:shadow-lg-dark rounded-lg" style="contain:content"><div class="bg-wash dark:bg-card-dark flex justify-between items-center relative z-10 border-b border-border dark:border-border-dark rounded-t-lg text-lg"><div class="flex-1 grow min-w-0 px-4 lg:px-6"><div><div class="relative overflow-hidden"><div class="w-[fit-content] invisible"><div class=" sp-tabs" translate="no"><div aria-label="Select active file" class=" sp-tabs-scrollable-container" role="tablist"><button aria-selected="true" class=" sp-tab-button" data-active="true" role="tab" title="/src/App.js" type="button">App.js</button></div></div></div><button class="absolute top-0 start-[2px]" id="headlessui-listbox-button-:Rj54cq6:" aria-haspopup="true" aria-expanded="false" data-headlessui-state=""><span class="h-full py-2 px-1 mt-px -mb-px flex border-b text-link dark:text-link-dark border-link dark:border-link-dark items-center text-md leading-tight truncate" style="max-width:160px">App.js</span></button></div></div></div><div class="px-3 flex items-center justify-end text-start" translate="yes"><button class="text-sm text-primary dark:text-primary-dark inline-flex items-center hover:text-link duration-100 ease-in transition mx-1" title="Reset Sandbox" type="button"><svg width="1em" height="1em" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg" class="inline mx-1 relative"><path d="M13.8982 5.20844C12.4626 4.88688 10.9686 4.93769 9.55821 5.35604L11.8524 3.06184C11.8989 3.0154 11.9357 2.96028 11.9608 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8.75979 20.1465 8.85355C20.2403 8.94732 20.3675 9 20.5001 9H21.5001C21.6327 9 21.7599 8.94732 21.8537 8.85355C21.9474 8.75979 22.0001 8.63261 22.0001 8.5V3.5C22.0001 3.10218 21.8421 2.72064 21.5608 2.43934C21.2795 2.15804 20.8979 2 20.5001 2V2Z" fill="currentColor"></path><path d="M21.5 13H20.5C20.3674 13 20.2402 13.0527 20.1464 13.1464C20.0527 13.2402 20 13.3674 20 13.5V20H4V4H10.5C10.6326 4 10.7598 3.94732 10.8536 3.85355C10.9473 3.75979 11 3.63261 11 3.5V2.5C11 2.36739 10.9473 2.24021 10.8536 2.14645C10.7598 2.05268 10.6326 2 10.5 2H3.5C3.10218 2 2.72064 2.15804 2.43934 2.43934C2.15804 2.72064 2 3.10218 2 3.5V20.5C2 20.8978 2.15804 21.2794 2.43934 21.5607C2.72064 21.842 3.10218 22 3.5 22H20.5C20.8978 22 21.2794 21.842 21.5607 21.5607C21.842 21.2794 22 20.8978 22 20.5V13.5C22 13.3674 21.9473 13.2402 21.8536 13.1464C21.7598 13.0527 21.6326 13 21.5 13Z" fill="currentColor"></path></svg><span class="hidden md:block">Fork</span></a></div></div><div class=" sp-layout"><div class=" sp-editor sp-stack"><div class=" sp-code-editor"><div aria-autocomplete="list" aria-label="Code Editor for App.js" aria-multiline="true" class="sp-pristine sp-javascript sp-cm" role="textbox" tabindex="0" translate="no"><pre class=" sp-pre-placeholder" style="margin-left:var(--sp-space-11)"><span class="sp-syntax-keyword">import</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-plain">useState</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'react'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">export</span> <span class="sp-syntax-keyword">default</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">Form</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">firstName</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">setFirstName</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useState</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">''</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">lastName</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">setLastName</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useState</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">''</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">fullName</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">setFullName</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useState</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">''</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">handleFirstNameChange</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">setFirstName</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span>.<span class="sp-syntax-property">target</span>.<span class="sp-syntax-property">value</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-definition">setFullName</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span>.<span class="sp-syntax-property">target</span>.<span class="sp-syntax-property">value</span> + <span class="sp-syntax-string">' '</span> + <span class="sp-syntax-plain">lastName</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">handleLastNameChange</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">setLastName</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span>.<span class="sp-syntax-property">target</span>.<span class="sp-syntax-property">value</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-definition">setFullName</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">firstName</span> + <span class="sp-syntax-string">' '</span> + <span class="sp-syntax-plain">e</span>.<span class="sp-syntax-property">target</span>.<span class="sp-syntax-property">value</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">h2</span><span class="sp-syntax-punctuation">></span>Let’s check you in<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">h2</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">label</span><span class="sp-syntax-punctuation">></span> First name:<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-string">' '</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">input</span> <span class="sp-syntax-property">value</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">firstName</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">onChange</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">handleFirstNameChange</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">label</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">label</span><span class="sp-syntax-punctuation">></span> Last name:<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-string">' '</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">input</span> <span class="sp-syntax-property">value</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">lastName</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">onChange</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">handleLastNameChange</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">label</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">p</span><span class="sp-syntax-punctuation">></span> Your ticket will be issued to: <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">b</span><span class="sp-syntax-punctuation">></span><span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">fullName</span><span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">b</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">p</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> </pre></div></div></div><div class=" order-last xl:order-2 sp-stack"><div class="p-0 sm:p-2 md:p-4 lg:p-8 bg-card dark:bg-wash-dark h-full relative md:rounded-b-lg lg:rounded-b-none"><div style="position:relative"><iframe class="rounded-t-none bg-white md:shadow-md sm:rounded-lg w-full max-w-full transition-opacity absolute opacity-0 pointer-events-none duration-75" title="Sandbox Preview" style="height:15px;z-index:-1"></iframe></div></div></div><button translate="yes" class="sandpack-expand flex text-base justify-between dark:border-card-dark bg-wash dark:bg-card-dark items-center z-10 p-1 w-full order-2 xl:order-last border-b-1 relative top-0"><span class="flex p-2 focus:outline-none text-primary dark:text-primary-dark leading-[20px]"><svg class="rotate-0 inline me-1.5 text-xl" xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg>Show more</span></button></div></div></div></div><div class="max-w-4xl ms-0 2xl:mx-auto"> <p class="whitespace-pre-wrap my-4">You can remove it and simplify the code by calculating <code dir="ltr" class="inline text-code text-secondary dark:text-secondary-dark px-1 rounded-md no-underline bg-gray-30 bg-opacity-10 py-px">fullName</code> while the component is rendering:</p> </div><div class="sandpack sandpack--playground w-full my-8" dir="ltr"><div class="sp-wrapper"><div class="shadow-lg dark:shadow-lg-dark rounded-lg" style="contain:content"><div class="bg-wash dark:bg-card-dark flex 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2.43934C2.15804 2.72064 2 3.10218 2 3.5V20.5C2 20.8978 2.15804 21.2794 2.43934 21.5607C2.72064 21.842 3.10218 22 3.5 22H20.5C20.8978 22 21.2794 21.842 21.5607 21.5607C21.842 21.2794 22 20.8978 22 20.5V13.5C22 13.3674 21.9473 13.2402 21.8536 13.1464C21.7598 13.0527 21.6326 13 21.5 13Z" fill="currentColor"></path></svg><span class="hidden md:block">Fork</span></a></div></div><div class=" sp-layout"><div class=" sp-editor sp-stack"><div class=" sp-code-editor"><div aria-autocomplete="list" aria-label="Code Editor for App.js" aria-multiline="true" class="sp-pristine sp-javascript sp-cm" role="textbox" tabindex="0" translate="no"><pre class=" sp-pre-placeholder" style="margin-left:var(--sp-space-11)"><span class="sp-syntax-keyword">import</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-plain">useState</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'react'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">export</span> <span class="sp-syntax-keyword">default</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">Form</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">firstName</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">setFirstName</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useState</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">''</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">lastName</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">setLastName</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useState</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">''</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-plain">fullName</span> = <span class="sp-syntax-plain">firstName</span> + <span class="sp-syntax-string">' '</span> + <span class="sp-syntax-plain">lastName</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">handleFirstNameChange</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">setFirstName</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span>.<span class="sp-syntax-property">target</span>.<span class="sp-syntax-property">value</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">handleLastNameChange</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">setLastName</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">e</span>.<span class="sp-syntax-property">target</span>.<span class="sp-syntax-property">value</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">h2</span><span class="sp-syntax-punctuation">></span>Let’s check you in<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">h2</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">label</span><span class="sp-syntax-punctuation">></span> First name:<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-string">' '</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">input</span> <span class="sp-syntax-property">value</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">firstName</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">onChange</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">handleFirstNameChange</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">label</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">label</span><span class="sp-syntax-punctuation">></span> Last name:<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-string">' '</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">input</span> <span class="sp-syntax-property">value</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">lastName</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">onChange</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">handleLastNameChange</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">label</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">p</span><span class="sp-syntax-punctuation">></span> Your ticket will be issued to: <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">b</span><span class="sp-syntax-punctuation">></span><span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">fullName</span><span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">b</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">p</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> </pre></div></div></div><div class=" order-last xl:order-2 sp-stack"><div class="p-0 sm:p-2 md:p-4 lg:p-8 bg-card dark:bg-wash-dark h-full relative md:rounded-b-lg lg:rounded-b-none"><div style="position:relative"><iframe class="rounded-t-none bg-white md:shadow-md sm:rounded-lg w-full max-w-full transition-opacity absolute opacity-0 pointer-events-none duration-75" title="Sandbox Preview" style="height:15px;z-index:-1"></iframe></div></div></div><button translate="yes" class="sandpack-expand flex text-base justify-between dark:border-card-dark bg-wash dark:bg-card-dark items-center z-10 p-1 w-full order-2 xl:order-last border-b-1 relative top-0"><span class="flex p-2 focus:outline-none text-primary dark:text-primary-dark leading-[20px]"><svg class="rotate-0 inline me-1.5 text-xl" xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg>Show more</span></button></div></div></div></div><div class="max-w-4xl ms-0 2xl:mx-auto"> <p class="whitespace-pre-wrap my-4">This might seem like a small change, but many bugs in React apps are fixed this way.</p> <section class="p-8 mt-16 mb-16 flex flex-row shadow-inner-border dark:shadow-inner-border-dark justify-between items-center bg-card dark:bg-card-dark rounded-2xl"><div class="flex-col"><h2 class="text-primary font-display dark:text-primary-dark font-bold text-2xl leading-tight">Ready to learn this topic?</h2><p class="whitespace-pre-wrap my-4">Read <strong class="font-bold"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/choosing-the-state-structure">Choosing the State Structure</a></strong> to learn how to design the state shape to avoid bugs.</p><a class="mt-1 active:scale-[.98] transition-transform inline-flex font-bold items-center outline-none focus:outline-none focus-visible:outline focus-visible:outline-link focus:outline-offset-2 focus-visible:dark:focus:outline-link-dark leading-snug bg-link text-white dark:bg-brand-dark dark:text-secondary hover:bg-opacity-80 text-base rounded-full px-4 py-2" aria-label="Read More" target="_self" href="/learn/choosing-the-state-structure">Read More<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" class="duration-100 ease-in transition -rotate-90 rtl:rotate-90 inline ms-1" style="min-width:20px;min-height:20px"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg></a></div></section><hr class="border-border dark:border-border-dark mb-14"/> <h2 id="sharing-state-between-components" class="mdx-heading text-3xl font-display leading-10 text-primary dark:text-primary-dark font-bold my-6">Sharing state between components <a href="#sharing-state-between-components" aria-label="Link for Sharing state between components " title="Link for Sharing state between components " class="mdx-header-anchor inline-block"><svg width="1em" height="1em" viewBox="0 0 13 13" xmlns="http://www.w3.org/2000/svg" class="text-gray-70 ms-2 h-5 w-5"><g fill="currentColor" fill-rule="evenodd"><path d="M7.778 7.975a2.5 2.5 0 0 0 .347-3.837L6.017 2.03a2.498 2.498 0 0 0-3.542-.007 2.5 2.5 0 0 0 .006 3.543l1.153 1.15c.07-.29.154-.563.25-.773.036-.077.084-.16.14-.25L3.18 4.85a1.496 1.496 0 0 1 .002-2.12 1.496 1.496 0 0 1 2.12 0l2.124 2.123a1.496 1.496 0 0 1-.333 2.37c.16.246.42.504.685.752z"></path><path d="M5.657 4.557a2.5 2.5 0 0 0-.347 3.837l2.108 2.108a2.498 2.498 0 0 0 3.542.007 2.5 2.5 0 0 0-.006-3.543L9.802 5.815c-.07.29-.154.565-.25.774-.036.076-.084.16-.14.25l.842.84c.585.587.59 1.532 0 2.122-.587.585-1.532.59-2.12 0L6.008 7.68a1.496 1.496 0 0 1 .332-2.372c-.16-.245-.42-.503-.685-.75z"></path></g></svg></a></h2> <p class="whitespace-pre-wrap my-4">Sometimes, you want the state of two components to always change together. To do it, remove state from both of them, move it to their closest common parent, and then pass it down to them via props. This is known as “lifting state up”, and it’s one of the most common things you will do writing React code.</p> <p class="whitespace-pre-wrap my-4">In this example, only one panel should be active at a time. To achieve this, instead of keeping the active state inside each individual panel, the parent component holds the state and specifies the props for its children.</p> </div><div class="sandpack sandpack--playground w-full my-8" dir="ltr"><div class="sp-wrapper"><div class="shadow-lg dark:shadow-lg-dark rounded-lg" style="contain:content"><div class="bg-wash dark:bg-card-dark flex justify-between items-center relative z-10 border-b border-border dark:border-border-dark rounded-t-lg text-lg"><div class="flex-1 grow min-w-0 px-4 lg:px-6"><div><div class="relative overflow-hidden"><div class="w-[fit-content] invisible"><div class=" sp-tabs" translate="no"><div aria-label="Select active file" class=" sp-tabs-scrollable-container" role="tablist"><button aria-selected="true" class=" sp-tab-button" data-active="true" role="tab" title="/src/App.js" type="button">App.js</button></div></div></div><button class="absolute top-0 start-[2px]" id="headlessui-listbox-button-:Rj58cq6:" 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translate="no"><pre class=" sp-pre-placeholder" style="margin-left:var(--sp-space-11)"><span class="sp-syntax-keyword">import</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-plain">useState</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'react'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">export</span> <span class="sp-syntax-keyword">default</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">Accordion</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">activeIndex</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">setActiveIndex</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useState</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-static">0</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">h2</span><span class="sp-syntax-punctuation">></span>Almaty, Kazakhstan<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">h2</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Panel</span> <span class="sp-syntax-property">title</span>=<span class="sp-syntax-string">"About"</span> <span class="sp-syntax-property">isActive</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">activeIndex</span> === <span class="sp-syntax-static">0</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">onShow</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">=></span> <span class="sp-syntax-definition">setActiveIndex</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-static">0</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">></span> With a population of about 2 million, Almaty is Kazakhstan's largest city. From 1929 to 1997, it was its capital city. <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Panel</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Panel</span> <span class="sp-syntax-property">title</span>=<span class="sp-syntax-string">"Etymology"</span> <span class="sp-syntax-property">isActive</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">activeIndex</span> === <span class="sp-syntax-static">1</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">onShow</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">=></span> <span class="sp-syntax-definition">setActiveIndex</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-static">1</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">></span> The name comes from <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">span</span> <span class="sp-syntax-property">lang</span>=<span class="sp-syntax-string">"kk-KZ"</span><span class="sp-syntax-punctuation">></span>алма<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">span</span><span class="sp-syntax-punctuation">></span>, the Kazakh word for "apple" and is often translated as "full of apples". In fact, the region surrounding Almaty is thought to be the ancestral home of the apple, and the wild <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">i</span> <span class="sp-syntax-property">lang</span>=<span class="sp-syntax-string">"la"</span><span class="sp-syntax-punctuation">></span>Malus sieversii<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">i</span><span class="sp-syntax-punctuation">></span> is considered a likely candidate for the ancestor of the modern domestic apple. <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Panel</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">Panel</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">title</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">children</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">isActive</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">onShow</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">section</span> <span class="sp-syntax-property">className</span>=<span class="sp-syntax-string">"panel"</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">h3</span><span class="sp-syntax-punctuation">></span><span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">title</span><span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">h3</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">isActive</span> ? <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">p</span><span class="sp-syntax-punctuation">></span><span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">children</span><span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">p</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span> : <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">button</span> <span class="sp-syntax-property">onClick</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">onShow</span><span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">></span> Show <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">button</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">section</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> </pre></div></div></div><div class=" order-last xl:order-2 sp-stack"><div class="p-0 sm:p-2 md:p-4 lg:p-8 bg-card dark:bg-wash-dark h-full relative md:rounded-b-lg lg:rounded-b-none"><div style="position:relative"><iframe class="rounded-t-none bg-white md:shadow-md sm:rounded-lg w-full 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lift state up and keep components in sync.</p><a class="mt-1 active:scale-[.98] transition-transform inline-flex font-bold items-center outline-none focus:outline-none focus-visible:outline focus-visible:outline-link focus:outline-offset-2 focus-visible:dark:focus:outline-link-dark leading-snug bg-link text-white dark:bg-brand-dark dark:text-secondary hover:bg-opacity-80 text-base rounded-full px-4 py-2" aria-label="Read More" target="_self" href="/learn/sharing-state-between-components">Read More<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" class="duration-100 ease-in transition -rotate-90 rtl:rotate-90 inline ms-1" style="min-width:20px;min-height:20px"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg></a></div></section><hr class="border-border dark:border-border-dark mb-14"/> <h2 id="preserving-and-resetting-state" class="mdx-heading text-3xl font-display leading-10 text-primary dark:text-primary-dark font-bold my-6">Preserving and resetting state <a href="#preserving-and-resetting-state" aria-label="Link for Preserving and resetting state " title="Link for Preserving and resetting state " class="mdx-header-anchor inline-block"><svg width="1em" height="1em" viewBox="0 0 13 13" xmlns="http://www.w3.org/2000/svg" class="text-gray-70 ms-2 h-5 w-5"><g fill="currentColor" fill-rule="evenodd"><path d="M7.778 7.975a2.5 2.5 0 0 0 .347-3.837L6.017 2.03a2.498 2.498 0 0 0-3.542-.007 2.5 2.5 0 0 0 .006 3.543l1.153 1.15c.07-.29.154-.563.25-.773.036-.077.084-.16.14-.25L3.18 4.85a1.496 1.496 0 0 1 .002-2.12 1.496 1.496 0 0 1 2.12 0l2.124 2.123a1.496 1.496 0 0 1-.333 2.37c.16.246.42.504.685.752z"></path><path d="M5.657 4.557a2.5 2.5 0 0 0-.347 3.837l2.108 2.108a2.498 2.498 0 0 0 3.542.007 2.5 2.5 0 0 0-.006-3.543L9.802 5.815c-.07.29-.154.565-.25.774-.036.076-.084.16-.14.25l.842.84c.585.587.59 1.532 0 2.122-.587.585-1.532.59-2.12 0L6.008 7.68a1.496 1.496 0 0 1 .332-2.372c-.16-.245-.42-.503-.685-.75z"></path></g></svg></a></h2> <p class="whitespace-pre-wrap my-4">When you re-render a component, React needs to decide which parts of the tree to keep (and update), and which parts to discard or re-create from scratch. In most cases, React’s automatic behavior works well enough. By default, React preserves the parts of the tree that “match up” with the previously rendered component tree.</p> <p class="whitespace-pre-wrap my-4">However, sometimes this is not what you want. In this chat app, typing a message and then switching the recipient does not reset the input. This can make the user accidentally send a message to the wrong person:</p> </div><div class="sandpack sandpack--playground w-full my-8" dir="ltr"><div class="sp-wrapper"><div class="shadow-lg dark:shadow-lg-dark rounded-lg" style="contain:content"><div class="bg-wash dark:bg-card-dark flex justify-between items-center relative z-10 border-b border-border dark:border-border-dark rounded-t-lg text-lg"><div class="flex-1 grow min-w-0 px-4 lg:px-6"><div><div class="relative overflow-hidden"><div class="w-[fit-content] invisible"><div class=" sp-tabs" translate="no"><div aria-label="Select active file" class=" sp-tabs-scrollable-container" role="tablist"><button aria-selected="true" class=" sp-tab-button" data-active="true" role="tab" title="/src/App.js" type="button">App.js</button><button aria-selected="false" class=" sp-tab-button" data-active="false" role="tab" title="/src/ContactList.js" type="button">ContactList.js</button><button aria-selected="false" class=" sp-tab-button" data-active="false" role="tab" title="/src/Chat.js" type="button">Chat.js</button></div></div></div><button class="absolute top-0 start-[2px]" id="headlessui-listbox-button-:Rj5acq6:" aria-haspopup="true" aria-expanded="false" data-headlessui-state=""><span class="h-full py-2 px-1 mt-px -mb-px flex border-b text-link dark:text-link-dark border-link dark:border-link-dark items-center text-md leading-tight truncate" style="max-width:160px">App.js<span class="ms-2"><svg class="rotate-0" xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 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translate="no"><pre class=" sp-pre-placeholder" style="margin-left:var(--sp-space-11)"><span class="sp-syntax-keyword">import</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-plain">useState</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'react'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">import</span> <span class="sp-syntax-plain">Chat</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'./Chat.js'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">import</span> <span class="sp-syntax-plain">ContactList</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'./ContactList.js'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">export</span> <span class="sp-syntax-keyword">default</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">Messenger</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">to</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">setTo</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useState</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">contacts</span><span class="sp-syntax-punctuation">[</span><span class="sp-syntax-static">0</span><span class="sp-syntax-punctuation">]</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">div</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">ContactList</span> <span class="sp-syntax-property">contacts</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">contacts</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">selectedContact</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">to</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">onSelect</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">contact</span> <span class="sp-syntax-punctuation">=></span> <span class="sp-syntax-definition">setTo</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">contact</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Chat</span> <span class="sp-syntax-property">contact</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">to</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">div</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-plain">contacts</span> = <span class="sp-syntax-punctuation">[</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">name</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'Taylor'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">email</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'taylor@mail.com'</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">name</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'Alice'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">email</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'alice@mail.com'</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">name</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'Bob'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">email</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'bob@mail.com'</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">]</span><span class="sp-syntax-punctuation">;</span> </pre></div></div></div><div class=" order-last xl:order-2 sp-stack"><div class="p-0 sm:p-2 md:p-4 lg:p-8 bg-card dark:bg-wash-dark h-full relative md:rounded-b-lg lg:rounded-b-none"><div style="position:relative"><iframe class="rounded-t-none bg-white md:shadow-md sm:rounded-lg w-full max-w-full transition-opacity absolute opacity-0 pointer-events-none duration-75" title="Sandbox Preview" style="height:15px;z-index:-1"></iframe></div></div></div><button translate="yes" class="sandpack-expand flex text-base justify-between dark:border-card-dark bg-wash dark:bg-card-dark items-center z-10 p-1 w-full order-2 xl:order-last border-b-1 relative top-0"><span class="flex p-2 focus:outline-none text-primary dark:text-primary-dark leading-[20px]"><svg class="rotate-0 inline me-1.5 text-xl" xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20"><g 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px-1 rounded-md no-underline bg-gray-30 bg-opacity-10 py-px">key</code>, like <code dir="ltr" class="inline text-code text-secondary dark:text-secondary-dark px-1 rounded-md no-underline bg-gray-30 bg-opacity-10 py-px"><Chat key={email} /></code>. This tells React that if the recipient is different, it should be considered a <em>different</em> <code dir="ltr" class="inline text-code text-secondary dark:text-secondary-dark px-1 rounded-md no-underline bg-gray-30 bg-opacity-10 py-px">Chat</code> component that needs to be re-created from scratch with the new data (and UI like inputs). Now switching between the recipients resets the input field—even though you render the same component.</p> </div><div class="sandpack sandpack--playground w-full my-8" dir="ltr"><div class="sp-wrapper"><div class="shadow-lg dark:shadow-lg-dark rounded-lg" style="contain:content"><div class="bg-wash dark:bg-card-dark flex justify-between items-center relative z-10 border-b border-border dark:border-border-dark rounded-t-lg text-lg"><div class="flex-1 grow min-w-0 px-4 lg:px-6"><div><div class="relative overflow-hidden"><div class="w-[fit-content] invisible"><div class=" sp-tabs" translate="no"><div aria-label="Select active file" class=" sp-tabs-scrollable-container" role="tablist"><button aria-selected="true" class=" sp-tab-button" data-active="true" role="tab" title="/src/App.js" type="button">App.js</button><button aria-selected="false" class=" sp-tab-button" data-active="false" role="tab" title="/src/ContactList.js" type="button">ContactList.js</button><button aria-selected="false" 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translate="no"><pre class=" sp-pre-placeholder" style="margin-left:var(--sp-space-11)"><span class="sp-syntax-keyword">import</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-plain">useState</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'react'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">import</span> <span class="sp-syntax-plain">Chat</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'./Chat.js'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">import</span> <span class="sp-syntax-plain">ContactList</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'./ContactList.js'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">export</span> <span class="sp-syntax-keyword">default</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">Messenger</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">to</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">setTo</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useState</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">contacts</span><span class="sp-syntax-punctuation">[</span><span class="sp-syntax-static">0</span><span class="sp-syntax-punctuation">]</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">div</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">ContactList</span> <span class="sp-syntax-property">contacts</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">contacts</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">selectedContact</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">to</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">onSelect</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">contact</span> <span class="sp-syntax-punctuation">=></span> <span class="sp-syntax-definition">setTo</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">contact</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Chat</span> <span class="sp-syntax-property">key</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">to</span>.<span class="sp-syntax-property">email</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">contact</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">to</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">div</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-plain">contacts</span> = <span class="sp-syntax-punctuation">[</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">name</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'Taylor'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">email</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'taylor@mail.com'</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">name</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'Alice'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">email</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'alice@mail.com'</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">name</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'Bob'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">email</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'bob@mail.com'</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">]</span><span class="sp-syntax-punctuation">;</span> </pre></div></div></div><div class=" order-last xl:order-2 sp-stack"><div class="p-0 sm:p-2 md:p-4 lg:p-8 bg-card dark:bg-wash-dark h-full relative md:rounded-b-lg lg:rounded-b-none"><div style="position:relative"><iframe class="rounded-t-none bg-white md:shadow-md sm:rounded-lg w-full max-w-full transition-opacity absolute opacity-0 pointer-events-none duration-75" title="Sandbox Preview" style="height:15px;z-index:-1"></iframe></div></div></div><button translate="yes" class="sandpack-expand flex text-base justify-between dark:border-card-dark bg-wash dark:bg-card-dark items-center z-10 p-1 w-full order-2 xl:order-last border-b-1 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<section class="p-8 mt-16 mb-16 flex flex-row shadow-inner-border dark:shadow-inner-border-dark justify-between items-center bg-card dark:bg-card-dark rounded-2xl"><div class="flex-col"><h2 class="text-primary font-display dark:text-primary-dark font-bold text-2xl leading-tight">Ready to learn this topic?</h2><p class="whitespace-pre-wrap my-4">Read <strong class="font-bold"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/preserving-and-resetting-state">Preserving and Resetting State</a></strong> to learn the lifetime of state and how to control it.</p><a class="mt-1 active:scale-[.98] transition-transform inline-flex font-bold items-center outline-none focus:outline-none focus-visible:outline focus-visible:outline-link focus:outline-offset-2 focus-visible:dark:focus:outline-link-dark leading-snug bg-link text-white dark:bg-brand-dark dark:text-secondary 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398"></polygon></g></svg></a></div></section><hr class="border-border dark:border-border-dark mb-14"/> <h2 id="extracting-state-logic-into-a-reducer" class="mdx-heading text-3xl font-display leading-10 text-primary dark:text-primary-dark font-bold my-6">Extracting state logic into a reducer <a href="#extracting-state-logic-into-a-reducer" aria-label="Link for Extracting state logic into a reducer " title="Link for Extracting state logic into a reducer " class="mdx-header-anchor inline-block"><svg width="1em" height="1em" viewBox="0 0 13 13" xmlns="http://www.w3.org/2000/svg" class="text-gray-70 ms-2 h-5 w-5"><g fill="currentColor" fill-rule="evenodd"><path d="M7.778 7.975a2.5 2.5 0 0 0 .347-3.837L6.017 2.03a2.498 2.498 0 0 0-3.542-.007 2.5 2.5 0 0 0 .006 3.543l1.153 1.15c.07-.29.154-.563.25-.773.036-.077.084-.16.14-.25L3.18 4.85a1.496 1.496 0 0 1 .002-2.12 1.496 1.496 0 0 1 2.12 0l2.124 2.123a1.496 1.496 0 0 1-.333 2.37c.16.246.42.504.685.752z"></path><path d="M5.657 4.557a2.5 2.5 0 0 0-.347 3.837l2.108 2.108a2.498 2.498 0 0 0 3.542.007 2.5 2.5 0 0 0-.006-3.543L9.802 5.815c-.07.29-.154.565-.25.774-.036.076-.084.16-.14.25l.842.84c.585.587.59 1.532 0 2.122-.587.585-1.532.59-2.12 0L6.008 7.68a1.496 1.496 0 0 1 .332-2.372c-.16-.245-.42-.503-.685-.75z"></path></g></svg></a></h2> <p class="whitespace-pre-wrap my-4">Components with many state updates spread across many event handlers can get overwhelming. For these cases, you can consolidate all the state update logic outside your component in a single function, called “reducer”. Your event handlers become concise because they only specify the user “actions”. At the bottom of the file, the reducer function specifies how the state should update in response to each action!</p> </div><div class="sandpack sandpack--playground w-full my-8" dir="ltr"><div class="sp-wrapper"><div class="shadow-lg dark:shadow-lg-dark rounded-lg" style="contain:content"><div class="bg-wash dark:bg-card-dark flex justify-between items-center relative z-10 border-b border-border dark:border-border-dark rounded-t-lg text-lg"><div class="flex-1 grow min-w-0 px-4 lg:px-6"><div><div class="relative overflow-hidden"><div class="w-[fit-content] invisible"><div class=" sp-tabs" translate="no"><div aria-label="Select active file" class=" sp-tabs-scrollable-container" role="tablist"><button aria-selected="true" class=" sp-tab-button" data-active="true" role="tab" title="/src/App.js" type="button">App.js</button></div></div></div><button class="absolute top-0 start-[2px]" id="headlessui-listbox-button-:Rj5ecq6:" aria-haspopup="true" aria-expanded="false" 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style="margin-left:var(--sp-space-11)"><span class="sp-syntax-keyword">import</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-plain">useReducer</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'react'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">import</span> <span class="sp-syntax-plain">AddTask</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'./AddTask.js'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">import</span> <span class="sp-syntax-plain">TaskList</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'./TaskList.js'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">export</span> <span class="sp-syntax-keyword">default</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">TaskApp</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-plain">tasks</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">dispatch</span><span class="sp-syntax-punctuation">]</span> = <span class="sp-syntax-definition">useReducer</span><span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-plain">tasksReducer</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">initialTasks</span> <span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">handleAddTask</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">text</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">dispatch</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">type</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'added'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">id</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-plain">nextId</span>++<span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">text</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-plain">text</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">handleChangeTask</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">task</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">dispatch</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">type</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'changed'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">task</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-plain">task</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">handleDeleteTask</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">taskId</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-definition">dispatch</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">type</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'deleted'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">id</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-plain">taskId</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">h1</span><span class="sp-syntax-punctuation">></span>Prague itinerary<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">h1</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">AddTask</span> <span class="sp-syntax-property">onAddTask</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">handleAddTask</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">TaskList</span> <span class="sp-syntax-property">tasks</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">tasks</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">onChangeTask</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">handleChangeTask</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-property">onDeleteTask</span>=<span class="sp-syntax-punctuation">{</span><span class="sp-syntax-plain">handleDeleteTask</span><span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">tasksReducer</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">tasks</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-plain">action</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">switch</span> <span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">action</span>.<span class="sp-syntax-property">type</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">case</span> <span class="sp-syntax-string">'added'</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation">[</span><span class="sp-syntax-punctuation">...</span><span class="sp-syntax-plain">tasks</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">id</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-plain">action</span>.<span class="sp-syntax-property">id</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">text</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-plain">action</span>.<span class="sp-syntax-property">text</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">done</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-static">false</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">]</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">case</span> <span class="sp-syntax-string">'changed'</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-plain">tasks</span>.<span class="sp-syntax-property">map</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">t</span> <span class="sp-syntax-punctuation">=></span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">if</span> <span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">t</span>.<span class="sp-syntax-property">id</span> === <span class="sp-syntax-plain">action</span>.<span class="sp-syntax-property">task</span>.<span class="sp-syntax-property">id</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-plain">action</span>.<span class="sp-syntax-property">task</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">else</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-plain">t</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">case</span> <span class="sp-syntax-string">'deleted'</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-plain">tasks</span>.<span class="sp-syntax-property">filter</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-plain">t</span> <span class="sp-syntax-punctuation">=></span> <span class="sp-syntax-plain">t</span>.<span class="sp-syntax-property">id</span> !== <span class="sp-syntax-plain">action</span>.<span class="sp-syntax-property">id</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">default</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">throw</span> <span class="sp-syntax-definition">Error</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-string">'Unknown action: '</span> + <span class="sp-syntax-plain">action</span>.<span class="sp-syntax-property">type</span><span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">let</span> <span class="sp-syntax-plain">nextId</span> = <span class="sp-syntax-static">3</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">const</span> <span class="sp-syntax-plain">initialTasks</span> = <span class="sp-syntax-punctuation">[</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">id</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-static">0</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">text</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'Visit Kafka Museum'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">done</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-static">true</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">id</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-static">1</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">text</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'Watch a puppet show'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">done</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-static">false</span> <span class="sp-syntax-punctuation">}</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-property">id</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-static">2</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">text</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-string">'Lennon Wall pic'</span><span class="sp-syntax-punctuation">,</span> <span class="sp-syntax-property">done</span><span class="sp-syntax-punctuation">:</span> <span class="sp-syntax-static">false</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-punctuation">]</span><span class="sp-syntax-punctuation">;</span> </pre></div></div></div><div class=" order-last xl:order-2 sp-stack"><div class="p-0 sm:p-2 md:p-4 lg:p-8 bg-card dark:bg-wash-dark h-full relative md:rounded-b-lg lg:rounded-b-none"><div style="position:relative"><iframe class="rounded-t-none bg-white md:shadow-md sm:rounded-lg w-full 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105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg>Show more</span></button></div></div></div></div><div class="max-w-4xl ms-0 2xl:mx-auto"> <section class="p-8 mt-16 mb-16 flex flex-row shadow-inner-border dark:shadow-inner-border-dark justify-between items-center bg-card dark:bg-card-dark rounded-2xl"><div class="flex-col"><h2 class="text-primary font-display dark:text-primary-dark font-bold text-2xl leading-tight">Ready to learn this topic?</h2><p class="whitespace-pre-wrap my-4">Read <strong class="font-bold"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/extracting-state-logic-into-a-reducer">Extracting State Logic into a Reducer</a></strong> to learn how to consolidate logic in the reducer function.</p><a class="mt-1 active:scale-[.98] transition-transform inline-flex font-bold items-center outline-none focus:outline-none focus-visible:outline focus-visible:outline-link focus:outline-offset-2 focus-visible:dark:focus:outline-link-dark leading-snug bg-link text-white dark:bg-brand-dark dark:text-secondary hover:bg-opacity-80 text-base rounded-full px-4 py-2" aria-label="Read More" target="_self" href="/learn/extracting-state-logic-into-a-reducer">Read More<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" class="duration-100 ease-in transition -rotate-90 rtl:rotate-90 inline ms-1" style="min-width:20px;min-height:20px"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg></a></div></section><hr class="border-border dark:border-border-dark mb-14"/> <h2 id="passing-data-deeply-with-context" class="mdx-heading text-3xl font-display leading-10 text-primary dark:text-primary-dark font-bold my-6">Passing data deeply with context <a href="#passing-data-deeply-with-context" aria-label="Link for Passing data deeply with context " title="Link for Passing data deeply with context " class="mdx-header-anchor inline-block"><svg width="1em" height="1em" viewBox="0 0 13 13" xmlns="http://www.w3.org/2000/svg" class="text-gray-70 ms-2 h-5 w-5"><g fill="currentColor" fill-rule="evenodd"><path d="M7.778 7.975a2.5 2.5 0 0 0 .347-3.837L6.017 2.03a2.498 2.498 0 0 0-3.542-.007 2.5 2.5 0 0 0 .006 3.543l1.153 1.15c.07-.29.154-.563.25-.773.036-.077.084-.16.14-.25L3.18 4.85a1.496 1.496 0 0 1 .002-2.12 1.496 1.496 0 0 1 2.12 0l2.124 2.123a1.496 1.496 0 0 1-.333 2.37c.16.246.42.504.685.752z"></path><path d="M5.657 4.557a2.5 2.5 0 0 0-.347 3.837l2.108 2.108a2.498 2.498 0 0 0 3.542.007 2.5 2.5 0 0 0-.006-3.543L9.802 5.815c-.07.29-.154.565-.25.774-.036.076-.084.16-.14.25l.842.84c.585.587.59 1.532 0 2.122-.587.585-1.532.59-2.12 0L6.008 7.68a1.496 1.496 0 0 1 .332-2.372c-.16-.245-.42-.503-.685-.75z"></path></g></svg></a></h2> <p class="whitespace-pre-wrap my-4">Usually, you will pass information from a parent component to a child component via props. But passing props can become inconvenient if you need to pass some prop through many components, or if many components need the same information. Context lets the parent component make some information available to any component in the tree below it—no matter how deep it is—without passing it explicitly through props.</p> <p class="whitespace-pre-wrap my-4">Here, the <code dir="ltr" class="inline text-code text-secondary dark:text-secondary-dark px-1 rounded-md no-underline bg-gray-30 bg-opacity-10 py-px">Heading</code> component determines its heading level by “asking” the closest <code dir="ltr" class="inline text-code text-secondary dark:text-secondary-dark px-1 rounded-md no-underline bg-gray-30 bg-opacity-10 py-px">Section</code> for its level. Each <code dir="ltr" class="inline text-code text-secondary dark:text-secondary-dark px-1 rounded-md no-underline bg-gray-30 bg-opacity-10 py-px">Section</code> tracks its own level by asking the parent <code dir="ltr" class="inline text-code text-secondary dark:text-secondary-dark px-1 rounded-md no-underline bg-gray-30 bg-opacity-10 py-px">Section</code> and adding one to it. Every <code dir="ltr" class="inline text-code text-secondary dark:text-secondary-dark px-1 rounded-md no-underline bg-gray-30 bg-opacity-10 py-px">Section</code> provides information to all components below it without passing props—it does that through context.</p> </div><div class="sandpack sandpack--playground w-full my-8" dir="ltr"><div class="sp-wrapper"><div class="shadow-lg dark:shadow-lg-dark rounded-lg" style="contain:content"><div class="bg-wash dark:bg-card-dark flex justify-between items-center relative z-10 border-b border-border dark:border-border-dark rounded-t-lg text-lg"><div class="flex-1 grow min-w-0 px-4 lg:px-6"><div><div class="relative overflow-hidden"><div class="w-[fit-content] invisible"><div class=" sp-tabs" translate="no"><div aria-label="Select active file" class=" sp-tabs-scrollable-container" role="tablist"><button aria-selected="true" class=" sp-tab-button" data-active="true" role="tab" title="/src/App.js" type="button">App.js</button><button 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13.0527 21.6326 13 21.5 13Z" fill="currentColor"></path></svg><span class="hidden md:block">Fork</span></a></div></div><div class=" sp-layout"><div class=" sp-editor sp-stack"><div class=" sp-code-editor"><div aria-autocomplete="list" aria-label="Code Editor for App.js" aria-multiline="true" class="sp-pristine sp-javascript sp-cm" role="textbox" tabindex="0" translate="no"><pre class=" sp-pre-placeholder" style="margin-left:var(--sp-space-11)"><span class="sp-syntax-keyword">import</span> <span class="sp-syntax-plain">Heading</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'./Heading.js'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">import</span> <span class="sp-syntax-plain">Section</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'./Section.js'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">export</span> <span class="sp-syntax-keyword">default</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">Page</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Section</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span>Title<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Section</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span>Heading<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span>Heading<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span>Heading<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Section</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span>Sub-heading<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span>Sub-heading<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span>Sub-heading<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Section</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span>Sub-sub-heading<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span>Sub-sub-heading<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span>Sub-sub-heading<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Heading</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Section</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Section</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Section</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">Section</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> </pre></div></div></div><div class=" order-last xl:order-2 sp-stack"><div class="p-0 sm:p-2 md:p-4 lg:p-8 bg-card dark:bg-wash-dark h-full relative md:rounded-b-lg lg:rounded-b-none"><div style="position:relative"><iframe class="rounded-t-none bg-white md:shadow-md sm:rounded-lg w-full max-w-full transition-opacity absolute opacity-0 pointer-events-none duration-75" title="Sandbox Preview" 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L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg>Show more</span></button></div></div></div></div><div class="max-w-4xl ms-0 2xl:mx-auto"> <section class="p-8 mt-16 mb-16 flex flex-row shadow-inner-border dark:shadow-inner-border-dark justify-between items-center bg-card dark:bg-card-dark rounded-2xl"><div class="flex-col"><h2 class="text-primary font-display dark:text-primary-dark font-bold text-2xl leading-tight">Ready to learn this topic?</h2><p class="whitespace-pre-wrap my-4">Read <strong class="font-bold"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/passing-data-deeply-with-context">Passing Data Deeply with Context</a></strong> to learn about using context as an alternative to passing props.</p><a class="mt-1 active:scale-[.98] transition-transform inline-flex font-bold items-center outline-none focus:outline-none focus-visible:outline focus-visible:outline-link focus:outline-offset-2 focus-visible:dark:focus:outline-link-dark leading-snug bg-link text-white dark:bg-brand-dark dark:text-secondary hover:bg-opacity-80 text-base rounded-full px-4 py-2" aria-label="Read More" target="_self" href="/learn/passing-data-deeply-with-context">Read More<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20" class="duration-100 ease-in transition -rotate-90 rtl:rotate-90 inline ms-1" style="min-width:20px;min-height:20px"><g fill="none" fill-rule="evenodd" transform="translate(-446 -398)"><path fill="currentColor" fill-rule="nonzero" d="M95.8838835,240.366117 C95.3957281,239.877961 94.6042719,239.877961 94.1161165,240.366117 C93.6279612,240.854272 93.6279612,241.645728 94.1161165,242.133883 L98.6161165,246.633883 C99.1042719,247.122039 99.8957281,247.122039 100.383883,246.633883 L104.883883,242.133883 C105.372039,241.645728 105.372039,240.854272 104.883883,240.366117 C104.395728,239.877961 103.604272,239.877961 103.116117,240.366117 L99.5,243.982233 L95.8838835,240.366117 Z" transform="translate(356.5 164.5)"></path><polygon points="446 418 466 418 466 398 446 398"></polygon></g></svg></a></div></section><hr class="border-border dark:border-border-dark mb-14"/> <h2 id="scaling-up-with-reducer-and-context" class="mdx-heading text-3xl font-display leading-10 text-primary dark:text-primary-dark font-bold my-6">Scaling up with reducer and context <a href="#scaling-up-with-reducer-and-context" aria-label="Link for Scaling up with reducer and context " title="Link for Scaling up with reducer and context " class="mdx-header-anchor inline-block"><svg width="1em" height="1em" viewBox="0 0 13 13" xmlns="http://www.w3.org/2000/svg" class="text-gray-70 ms-2 h-5 w-5"><g fill="currentColor" fill-rule="evenodd"><path d="M7.778 7.975a2.5 2.5 0 0 0 .347-3.837L6.017 2.03a2.498 2.498 0 0 0-3.542-.007 2.5 2.5 0 0 0 .006 3.543l1.153 1.15c.07-.29.154-.563.25-.773.036-.077.084-.16.14-.25L3.18 4.85a1.496 1.496 0 0 1 .002-2.12 1.496 1.496 0 0 1 2.12 0l2.124 2.123a1.496 1.496 0 0 1-.333 2.37c.16.246.42.504.685.752z"></path><path d="M5.657 4.557a2.5 2.5 0 0 0-.347 3.837l2.108 2.108a2.498 2.498 0 0 0 3.542.007 2.5 2.5 0 0 0-.006-3.543L9.802 5.815c-.07.29-.154.565-.25.774-.036.076-.084.16-.14.25l.842.84c.585.587.59 1.532 0 2.122-.587.585-1.532.59-2.12 0L6.008 7.68a1.496 1.496 0 0 1 .332-2.372c-.16-.245-.42-.503-.685-.75z"></path></g></svg></a></h2> <p class="whitespace-pre-wrap my-4">Reducers let you consolidate a component’s state update logic. Context lets you pass information deep down to other components. You can combine reducers and context together to manage state of a complex screen.</p> <p class="whitespace-pre-wrap my-4">With this approach, a parent component with complex state manages it with a reducer. Other components anywhere deep in the tree can read its state via context. They can also dispatch actions to update that state.</p> </div><div class="sandpack sandpack--playground w-full my-8" dir="ltr"><div class="sp-wrapper"><div class="shadow-lg dark:shadow-lg-dark rounded-lg" style="contain:content"><div class="bg-wash dark:bg-card-dark flex justify-between items-center relative z-10 border-b border-border dark:border-border-dark rounded-t-lg text-lg"><div class="flex-1 grow min-w-0 px-4 lg:px-6"><div><div class="relative overflow-hidden"><div class="w-[fit-content] invisible"><div class=" sp-tabs" translate="no"><div aria-label="Select active file" class=" sp-tabs-scrollable-container" role="tablist"><button aria-selected="true" class=" sp-tab-button" data-active="true" role="tab" title="/src/App.js" type="button">App.js</button><button aria-selected="false" class=" sp-tab-button" data-active="false" role="tab" title="/src/TasksContext.js" type="button">TasksContext.js</button><button aria-selected="false" class=" sp-tab-button" data-active="false" 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sp-code-editor"><div aria-autocomplete="list" aria-label="Code Editor for App.js" aria-multiline="true" class="sp-pristine sp-javascript sp-cm" role="textbox" tabindex="0" translate="no"><pre class=" sp-pre-placeholder" style="margin-left:var(--sp-space-11)"><span class="sp-syntax-keyword">import</span> <span class="sp-syntax-plain">AddTask</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'./AddTask.js'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">import</span> <span class="sp-syntax-plain">TaskList</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'./TaskList.js'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">import</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-plain">TasksProvider</span> <span class="sp-syntax-punctuation">}</span> <span class="sp-syntax-keyword">from</span> <span class="sp-syntax-string">'./TasksContext.js'</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-keyword">export</span> <span class="sp-syntax-keyword">default</span> <span class="sp-syntax-keyword">function</span> <span class="sp-syntax-definition">TaskApp</span><span class="sp-syntax-punctuation">(</span><span class="sp-syntax-punctuation">)</span> <span class="sp-syntax-punctuation">{</span> <span class="sp-syntax-keyword">return</span> <span class="sp-syntax-punctuation">(</span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">TasksProvider</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-tag">h1</span><span class="sp-syntax-punctuation">></span>Day off in Kyoto<span class="sp-syntax-punctuation"></</span><span class="sp-syntax-tag">h1</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">AddTask</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"><</span><span class="sp-syntax-definition">TaskList</span> <span class="sp-syntax-punctuation">/></span> <span class="sp-syntax-punctuation"></</span><span class="sp-syntax-definition">TasksProvider</span><span class="sp-syntax-punctuation">></span> <span class="sp-syntax-punctuation">)</span><span class="sp-syntax-punctuation">;</span> <span class="sp-syntax-punctuation">}</span> </pre></div></div></div><div class=" order-last xl:order-2 sp-stack"><div class="p-0 sm:p-2 md:p-4 lg:p-8 bg-card dark:bg-wash-dark h-full relative md:rounded-b-lg lg:rounded-b-none"><div style="position:relative"><iframe class="rounded-t-none bg-white md:shadow-md sm:rounded-lg w-full max-w-full transition-opacity absolute opacity-0 pointer-events-none duration-75" title="Sandbox Preview" style="height:15px;z-index:-1"></iframe></div></div></div></div></div></div></div><div class="max-w-4xl ms-0 2xl:mx-auto"> <section class="p-8 mt-16 mb-16 flex flex-row shadow-inner-border dark:shadow-inner-border-dark justify-between items-center bg-card dark:bg-card-dark rounded-2xl"><div class="flex-col"><h2 class="text-primary font-display dark:text-primary-dark font-bold text-2xl leading-tight">Ready to learn this topic?</h2><p class="whitespace-pre-wrap my-4">Read <strong class="font-bold"><a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/scaling-up-with-reducer-and-context">Scaling Up with Reducer and Context</a></strong> to learn how state management scales in a growing app.</p><a class="mt-1 active:scale-[.98] transition-transform inline-flex font-bold items-center outline-none focus:outline-none focus-visible:outline focus-visible:outline-link focus:outline-offset-2 focus-visible:dark:focus:outline-link-dark leading-snug bg-link text-white 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" class="mdx-header-anchor inline-block"><svg width="1em" height="1em" viewBox="0 0 13 13" xmlns="http://www.w3.org/2000/svg" class="text-gray-70 ms-2 h-5 w-5"><g fill="currentColor" fill-rule="evenodd"><path d="M7.778 7.975a2.5 2.5 0 0 0 .347-3.837L6.017 2.03a2.498 2.498 0 0 0-3.542-.007 2.5 2.5 0 0 0 .006 3.543l1.153 1.15c.07-.29.154-.563.25-.773.036-.077.084-.16.14-.25L3.18 4.85a1.496 1.496 0 0 1 .002-2.12 1.496 1.496 0 0 1 2.12 0l2.124 2.123a1.496 1.496 0 0 1-.333 2.37c.16.246.42.504.685.752z"></path><path d="M5.657 4.557a2.5 2.5 0 0 0-.347 3.837l2.108 2.108a2.498 2.498 0 0 0 3.542.007 2.5 2.5 0 0 0-.006-3.543L9.802 5.815c-.07.29-.154.565-.25.774-.036.076-.084.16-.14.25l.842.84c.585.587.59 1.532 0 2.122-.587.585-1.532.59-2.12 0L6.008 7.68a1.496 1.496 0 0 1 .332-2.372c-.16-.245-.42-.503-.685-.75z"></path></g></svg></a></h2> <p class="whitespace-pre-wrap my-4">Head over to <a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/reacting-to-input-with-state">Reacting to Input with State</a> to start reading this chapter page by page!</p> <p class="whitespace-pre-wrap my-4">Or, if you’re already familiar with these topics, why not read about <a class="inline text-link dark:text-link-dark border-b border-link border-opacity-0 hover:border-opacity-100 duration-100 ease-in transition leading-normal" href="/learn/escape-hatches">Escape Hatches</a>?</p></div></div><div class="grid grid-cols-1 gap-4 py-4 mx-auto max-w-7xl md:grid-cols-2 md:py-12"><a class="flex gap-x-4 md:gap-x-6 items-center w-full md:min-w-80 md:w-fit md:max-w-md px-4 md:px-5 py-6 border-2 border-transparent text-base leading-base text-link dark:text-link-dark rounded-lg group focus:text-link dark:focus:text-link-dark focus:bg-highlight focus:border-link dark:focus:bg-highlight-dark dark:focus:border-link-dark focus:border-opacity-100 focus:border-2 focus:ring-1 focus:ring-offset-4 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tracking-wide font-bold text-sm text-secondary dark:text-secondary-dark px-4 w-full">On this page</h2><div class="h-full overflow-y-auto ps-4 max-h-[calc(100vh-7.5rem)]" style="overscroll-behavior:contain"><ul class="space-y-2 pb-16"><li class="text-sm px-2 rounded-s-xl bg-highlight dark:bg-highlight-dark"><a class="text-link dark:text-link-dark font-bold block hover:text-link dark:hover:text-link-dark leading-normal py-2" href="#">Overview</a></li><li class="text-sm px-2 rounded-s-xl"><a class="text-secondary dark:text-secondary-dark block hover:text-link dark:hover:text-link-dark leading-normal py-2" href="#reacting-to-input-with-state">Reacting to input with state </a></li><li class="text-sm px-2 rounded-s-xl"><a class="text-secondary dark:text-secondary-dark block hover:text-link dark:hover:text-link-dark leading-normal py-2" href="#choosing-the-state-structure">Choosing the state structure </a></li><li class="text-sm px-2 rounded-s-xl"><a class="text-secondary dark:text-secondary-dark block hover:text-link dark:hover:text-link-dark leading-normal py-2" href="#sharing-state-between-components">Sharing state between components </a></li><li class="text-sm px-2 rounded-s-xl"><a class="text-secondary dark:text-secondary-dark block hover:text-link dark:hover:text-link-dark leading-normal py-2" href="#preserving-and-resetting-state">Preserving and resetting state </a></li><li class="text-sm px-2 rounded-s-xl"><a class="text-secondary dark:text-secondary-dark block hover:text-link dark:hover:text-link-dark leading-normal py-2" href="#extracting-state-logic-into-a-reducer">Extracting state logic into a reducer </a></li><li class="text-sm px-2 rounded-s-xl"><a class="text-secondary dark:text-secondary-dark block hover:text-link dark:hover:text-link-dark leading-normal py-2" href="#passing-data-deeply-with-context">Passing data deeply with context </a></li><li class="text-sm px-2 rounded-s-xl"><a class="text-secondary dark:text-secondary-dark block hover:text-link dark:hover:text-link-dark leading-normal py-2" href="#scaling-up-with-reducer-and-context">Scaling up with reducer and context </a></li><li class="text-sm px-2 rounded-s-xl"><a class="text-secondary dark:text-secondary-dark block hover:text-link dark:hover:text-link-dark leading-normal py-2" href="#whats-next">What’s next? </a></li></ul></div></nav></div></div></div><script id="__NEXT_DATA__" type="application/json">{"props":{"pageProps":{"toc":"[{\"url\":\"#\",\"text\":\"Overview\",\"depth\":2},{\"url\":\"#reacting-to-input-with-state\",\"depth\":2,\"text\":\"Reacting to input with state \"},{\"url\":\"#choosing-the-state-structure\",\"depth\":2,\"text\":\"Choosing the state structure \"},{\"url\":\"#sharing-state-between-components\",\"depth\":2,\"text\":\"Sharing state between components \"},{\"url\":\"#preserving-and-resetting-state\",\"depth\":2,\"text\":\"Preserving and resetting state \"},{\"url\":\"#extracting-state-logic-into-a-reducer\",\"depth\":2,\"text\":\"Extracting state logic into a reducer \"},{\"url\":\"#passing-data-deeply-with-context\",\"depth\":2,\"text\":\"Passing data deeply with context \"},{\"url\":\"#scaling-up-with-reducer-and-context\",\"depth\":2,\"text\":\"Scaling up with reducer and context \"},{\"url\":\"#whats-next\",\"depth\":2,\"text\":\"What’s next? \"}]","content":"[[\"$r\",\"MaxWidth\",\"10\",{\"children\":[[\"$r\",\"Intro\",null,{\"children\":[\"$r\",\"p\",null,{\"children\":\"As your application grows, it helps to be more intentional about how your state is organized and how the data flows between your components. Redundant or duplicate state is a common source of bugs. In this chapter, you’ll learn how to structure your state well, how to keep your state update logic maintainable, and how to share state between distant components.\"}]}],\"\\n\",[\"$r\",\"YouWillLearn\",null,{\"isChapter\":true,\"children\":[\"$r\",\"ul\",null,{\"children\":[\"\\n\",[\"$r\",\"li\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/reacting-to-input-with-state\",\"children\":\"How to think about UI changes as state changes\"}]}],\"\\n\",[\"$r\",\"li\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/choosing-the-state-structure\",\"children\":\"How to structure state well\"}]}],\"\\n\",[\"$r\",\"li\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/sharing-state-between-components\",\"children\":\"How to “lift state up” to share it between components\"}]}],\"\\n\",[\"$r\",\"li\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/preserving-and-resetting-state\",\"children\":\"How to control whether the state gets preserved or reset\"}]}],\"\\n\",[\"$r\",\"li\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/extracting-state-logic-into-a-reducer\",\"children\":\"How to consolidate complex state logic in a function\"}]}],\"\\n\",[\"$r\",\"li\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/passing-data-deeply-with-context\",\"children\":\"How to pass information without “prop drilling”\"}]}],\"\\n\",[\"$r\",\"li\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/scaling-up-with-reducer-and-context\",\"children\":\"How to scale state management as your app grows\"}]}],\"\\n\"]}]}],\"\\n\",[\"$r\",\"h2\",null,{\"id\":\"reacting-to-input-with-state\",\"children\":\"Reacting to input with state \"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":\"With React, you won’t modify the UI from code directly. For example, you won’t write commands like “disable the button”, “enable the button”, “show the success message”, etc. Instead, you will describe the UI you want to see for the different visual states of your component (“initial state”, “typing state”, “success state”), and then trigger the state changes in response to user input. This is similar to how designers think about UI.\"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":[\"Here is a quiz form built using React. Note how it uses the \",[\"$r\",\"code\",null,{\"children\":\"status\"}],\" state variable to determine whether to enable or disable the submit button, and whether to show the success message instead.\"]}],\"\\n\"]}],[\"$r\",\"Sandpack\",null,{\"children\":[[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"children\":\"import { useState } from 'react';\\n\\nexport default function Form() {\\n const [answer, setAnswer] = useState('');\\n const [error, setError] = useState(null);\\n const [status, setStatus] = useState('typing');\\n\\n if (status === 'success') {\\n return \u003ch1\u003eThat's right!\u003c/h1\u003e\\n }\\n\\n async function handleSubmit(e) {\\n e.preventDefault();\\n setStatus('submitting');\\n try {\\n await submitForm(answer);\\n setStatus('success');\\n } catch (err) {\\n setStatus('typing');\\n setError(err);\\n }\\n }\\n\\n function handleTextareaChange(e) {\\n setAnswer(e.target.value);\\n }\\n\\n return (\\n \u003c\u003e\\n \u003ch2\u003eCity quiz\u003c/h2\u003e\\n \u003cp\u003e\\n In which city is there a billboard that turns air into drinkable water?\\n \u003c/p\u003e\\n \u003cform onSubmit={handleSubmit}\u003e\\n \u003ctextarea\\n value={answer}\\n onChange={handleTextareaChange}\\n disabled={status === 'submitting'}\\n /\u003e\\n \u003cbr /\u003e\\n \u003cbutton disabled={\\n answer.length === 0 ||\\n status === 'submitting'\\n }\u003e\\n Submit\\n \u003c/button\u003e\\n {error !== null \u0026\u0026\\n \u003cp className=\\\"Error\\\"\u003e\\n {error.message}\\n \u003c/p\u003e\\n }\\n \u003c/form\u003e\\n \u003c/\u003e\\n );\\n}\\n\\nfunction submitForm(answer) {\\n // Pretend it's hitting the network.\\n return new Promise((resolve, reject) =\u003e {\\n setTimeout(() =\u003e {\\n let shouldError = answer.toLowerCase() !== 'lima'\\n if (shouldError) {\\n reject(new Error('Good guess but a wrong answer. Try again!'));\\n } else {\\n resolve();\\n }\\n }, 1500);\\n });\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-css\",\"children\":\".Error { color: red; }\\n\"}]}]]}],[\"$r\",\"MaxWidth\",\"20\",{\"children\":[\"\\n\",[\"$r\",\"LearnMore\",null,{\"path\":\"/learn/reacting-to-input-with-state\",\"children\":[\"$r\",\"p\",null,{\"children\":[\"Read \",[\"$r\",\"strong\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/reacting-to-input-with-state\",\"children\":\"Reacting to Input with State\"}]}],\" to learn how to approach interactions with a state-driven mindset.\"]}]}],\"\\n\",[\"$r\",\"h2\",null,{\"id\":\"choosing-the-state-structure\",\"children\":\"Choosing the state structure \"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":\"Structuring state well can make a difference between a component that is pleasant to modify and debug, and one that is a constant source of bugs. The most important principle is that state shouldn’t contain redundant or duplicated information. If there’s unnecessary state, it’s easy to forget to update it, and introduce bugs!\"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":[\"For example, this form has a \",[\"$r\",\"strong\",null,{\"children\":\"redundant\"}],\" \",[\"$r\",\"code\",null,{\"children\":\"fullName\"}],\" state variable:\"]}],\"\\n\"]}],[\"$r\",\"Sandpack\",null,{\"children\":[[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"children\":\"import { useState } from 'react';\\n\\nexport default function Form() {\\n const [firstName, setFirstName] = useState('');\\n const [lastName, setLastName] = useState('');\\n const [fullName, setFullName] = useState('');\\n\\n function handleFirstNameChange(e) {\\n setFirstName(e.target.value);\\n setFullName(e.target.value + ' ' + lastName);\\n }\\n\\n function handleLastNameChange(e) {\\n setLastName(e.target.value);\\n setFullName(firstName + ' ' + e.target.value);\\n }\\n\\n return (\\n \u003c\u003e\\n \u003ch2\u003eLet’s check you in\u003c/h2\u003e\\n \u003clabel\u003e\\n First name:{' '}\\n \u003cinput\\n value={firstName}\\n onChange={handleFirstNameChange}\\n /\u003e\\n \u003c/label\u003e\\n \u003clabel\u003e\\n Last name:{' '}\\n \u003cinput\\n value={lastName}\\n onChange={handleLastNameChange}\\n /\u003e\\n \u003c/label\u003e\\n \u003cp\u003e\\n Your ticket will be issued to: \u003cb\u003e{fullName}\u003c/b\u003e\\n \u003c/p\u003e\\n \u003c/\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-css\",\"children\":\"label { display: block; margin-bottom: 5px; }\\n\"}]}]]}],[\"$r\",\"MaxWidth\",\"24\",{\"children\":[\"\\n\",[\"$r\",\"p\",null,{\"children\":[\"You can remove it and simplify the code by calculating \",[\"$r\",\"code\",null,{\"children\":\"fullName\"}],\" while the component is rendering:\"]}],\"\\n\"]}],[\"$r\",\"Sandpack\",null,{\"children\":[[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"children\":\"import { useState } from 'react';\\n\\nexport default function Form() {\\n const [firstName, setFirstName] = useState('');\\n const [lastName, setLastName] = useState('');\\n\\n const fullName = firstName + ' ' + lastName;\\n\\n function handleFirstNameChange(e) {\\n setFirstName(e.target.value);\\n }\\n\\n function handleLastNameChange(e) {\\n setLastName(e.target.value);\\n }\\n\\n return (\\n \u003c\u003e\\n \u003ch2\u003eLet’s check you in\u003c/h2\u003e\\n \u003clabel\u003e\\n First name:{' '}\\n \u003cinput\\n value={firstName}\\n onChange={handleFirstNameChange}\\n /\u003e\\n \u003c/label\u003e\\n \u003clabel\u003e\\n Last name:{' '}\\n \u003cinput\\n value={lastName}\\n onChange={handleLastNameChange}\\n /\u003e\\n \u003c/label\u003e\\n \u003cp\u003e\\n Your ticket will be issued to: \u003cb\u003e{fullName}\u003c/b\u003e\\n \u003c/p\u003e\\n \u003c/\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-css\",\"children\":\"label { display: block; margin-bottom: 5px; }\\n\"}]}]]}],[\"$r\",\"MaxWidth\",\"36\",{\"children\":[\"\\n\",[\"$r\",\"p\",null,{\"children\":\"This might seem like a small change, but many bugs in React apps are fixed this way.\"}],\"\\n\",[\"$r\",\"LearnMore\",null,{\"path\":\"/learn/choosing-the-state-structure\",\"children\":[\"$r\",\"p\",null,{\"children\":[\"Read \",[\"$r\",\"strong\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/choosing-the-state-structure\",\"children\":\"Choosing the State Structure\"}]}],\" to learn how to design the state shape to avoid bugs.\"]}]}],\"\\n\",[\"$r\",\"h2\",null,{\"id\":\"sharing-state-between-components\",\"children\":\"Sharing state between components \"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":\"Sometimes, you want the state of two components to always change together. To do it, remove state from both of them, move it to their closest common parent, and then pass it down to them via props. This is known as “lifting state up”, and it’s one of the most common things you will do writing React code.\"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":\"In this example, only one panel should be active at a time. To achieve this, instead of keeping the active state inside each individual panel, the parent component holds the state and specifies the props for its children.\"}],\"\\n\"]}],[\"$r\",\"Sandpack\",null,{\"children\":[[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"children\":\"import { useState } from 'react';\\n\\nexport default function Accordion() {\\n const [activeIndex, setActiveIndex] = useState(0);\\n return (\\n \u003c\u003e\\n \u003ch2\u003eAlmaty, Kazakhstan\u003c/h2\u003e\\n \u003cPanel\\n title=\\\"About\\\"\\n isActive={activeIndex === 0}\\n onShow={() =\u003e setActiveIndex(0)}\\n \u003e\\n With a population of about 2 million, Almaty is Kazakhstan's largest city. From 1929 to 1997, it was its capital city.\\n \u003c/Panel\u003e\\n \u003cPanel\\n title=\\\"Etymology\\\"\\n isActive={activeIndex === 1}\\n onShow={() =\u003e setActiveIndex(1)}\\n \u003e\\n The name comes from \u003cspan lang=\\\"kk-KZ\\\"\u003eалма\u003c/span\u003e, the Kazakh word for \\\"apple\\\" and is often translated as \\\"full of apples\\\". In fact, the region surrounding Almaty is thought to be the ancestral home of the apple, and the wild \u003ci lang=\\\"la\\\"\u003eMalus sieversii\u003c/i\u003e is considered a likely candidate for the ancestor of the modern domestic apple.\\n \u003c/Panel\u003e\\n \u003c/\u003e\\n );\\n}\\n\\nfunction Panel({\\n title,\\n children,\\n isActive,\\n onShow\\n}) {\\n return (\\n \u003csection className=\\\"panel\\\"\u003e\\n \u003ch3\u003e{title}\u003c/h3\u003e\\n {isActive ? (\\n \u003cp\u003e{children}\u003c/p\u003e\\n ) : (\\n \u003cbutton onClick={onShow}\u003e\\n Show\\n \u003c/button\u003e\\n )}\\n \u003c/section\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-css\",\"children\":\"h3, p { margin: 5px 0px; }\\n.panel {\\n padding: 10px;\\n border: 1px solid #aaa;\\n}\\n\"}]}]]}],[\"$r\",\"MaxWidth\",\"46\",{\"children\":[\"\\n\",[\"$r\",\"LearnMore\",null,{\"path\":\"/learn/sharing-state-between-components\",\"children\":[\"$r\",\"p\",null,{\"children\":[\"Read \",[\"$r\",\"strong\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/sharing-state-between-components\",\"children\":\"Sharing State Between Components\"}]}],\" to learn how to lift state up and keep components in sync.\"]}]}],\"\\n\",[\"$r\",\"h2\",null,{\"id\":\"preserving-and-resetting-state\",\"children\":\"Preserving and resetting state \"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":\"When you re-render a component, React needs to decide which parts of the tree to keep (and update), and which parts to discard or re-create from scratch. In most cases, React’s automatic behavior works well enough. By default, React preserves the parts of the tree that “match up” with the previously rendered component tree.\"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":\"However, sometimes this is not what you want. In this chat app, typing a message and then switching the recipient does not reset the input. This can make the user accidentally send a message to the wrong person:\"}],\"\\n\"]}],[\"$r\",\"Sandpack\",null,{\"children\":[[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/App.js\",\"children\":\"import { useState } from 'react';\\nimport Chat from './Chat.js';\\nimport ContactList from './ContactList.js';\\n\\nexport default function Messenger() {\\n const [to, setTo] = useState(contacts[0]);\\n return (\\n \u003cdiv\u003e\\n \u003cContactList\\n contacts={contacts}\\n selectedContact={to}\\n onSelect={contact =\u003e setTo(contact)}\\n /\u003e\\n \u003cChat contact={to} /\u003e\\n \u003c/div\u003e\\n )\\n}\\n\\nconst contacts = [\\n { name: 'Taylor', email: 'taylor@mail.com' },\\n { name: 'Alice', email: 'alice@mail.com' },\\n { name: 'Bob', email: 'bob@mail.com' }\\n];\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/ContactList.js\",\"children\":\"export default function ContactList({\\n selectedContact,\\n contacts,\\n onSelect\\n}) {\\n return (\\n \u003csection className=\\\"contact-list\\\"\u003e\\n \u003cul\u003e\\n {contacts.map(contact =\u003e\\n \u003cli key={contact.email}\u003e\\n \u003cbutton onClick={() =\u003e {\\n onSelect(contact);\\n }}\u003e\\n {contact.name}\\n \u003c/button\u003e\\n \u003c/li\u003e\\n )}\\n \u003c/ul\u003e\\n \u003c/section\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/Chat.js\",\"children\":\"import { useState } from 'react';\\n\\nexport default function Chat({ contact }) {\\n const [text, setText] = useState('');\\n return (\\n \u003csection className=\\\"chat\\\"\u003e\\n \u003ctextarea\\n value={text}\\n placeholder={'Chat to ' + contact.name}\\n onChange={e =\u003e setText(e.target.value)}\\n /\u003e\\n \u003cbr /\u003e\\n \u003cbutton\u003eSend to {contact.email}\u003c/button\u003e\\n \u003c/section\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-css\",\"children\":\".chat, .contact-list {\\n float: left;\\n margin-bottom: 20px;\\n}\\nul, li {\\n list-style: none;\\n margin: 0;\\n padding: 0;\\n}\\nli button {\\n width: 100px;\\n padding: 10px;\\n margin-right: 10px;\\n}\\ntextarea {\\n height: 150px;\\n}\\n\"}]}]]}],[\"$r\",\"MaxWidth\",\"50\",{\"children\":[\"\\n\",[\"$r\",\"p\",null,{\"children\":[\"React lets you override the default behavior, and \",[\"$r\",\"em\",null,{\"children\":\"force\"}],\" a component to reset its state by passing it a different \",[\"$r\",\"code\",null,{\"children\":\"key\"}],\", like \",[\"$r\",\"code\",null,{\"children\":\"\u003cChat key={email} /\u003e\"}],\". This tells React that if the recipient is different, it should be considered a \",[\"$r\",\"em\",null,{\"children\":\"different\"}],\" \",[\"$r\",\"code\",null,{\"children\":\"Chat\"}],\" component that needs to be re-created from scratch with the new data (and UI like inputs). Now switching between the recipients resets the input field—even though you render the same component.\"]}],\"\\n\"]}],[\"$r\",\"Sandpack\",null,{\"children\":[[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/App.js\",\"children\":\"import { useState } from 'react';\\nimport Chat from './Chat.js';\\nimport ContactList from './ContactList.js';\\n\\nexport default function Messenger() {\\n const [to, setTo] = useState(contacts[0]);\\n return (\\n \u003cdiv\u003e\\n \u003cContactList\\n contacts={contacts}\\n selectedContact={to}\\n onSelect={contact =\u003e setTo(contact)}\\n /\u003e\\n \u003cChat key={to.email} contact={to} /\u003e\\n \u003c/div\u003e\\n )\\n}\\n\\nconst contacts = [\\n { name: 'Taylor', email: 'taylor@mail.com' },\\n { name: 'Alice', email: 'alice@mail.com' },\\n { name: 'Bob', email: 'bob@mail.com' }\\n];\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/ContactList.js\",\"children\":\"export default function ContactList({\\n selectedContact,\\n contacts,\\n onSelect\\n}) {\\n return (\\n \u003csection className=\\\"contact-list\\\"\u003e\\n \u003cul\u003e\\n {contacts.map(contact =\u003e\\n \u003cli key={contact.email}\u003e\\n \u003cbutton onClick={() =\u003e {\\n onSelect(contact);\\n }}\u003e\\n {contact.name}\\n \u003c/button\u003e\\n \u003c/li\u003e\\n )}\\n \u003c/ul\u003e\\n \u003c/section\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/Chat.js\",\"children\":\"import { useState } from 'react';\\n\\nexport default function Chat({ contact }) {\\n const [text, setText] = useState('');\\n return (\\n \u003csection className=\\\"chat\\\"\u003e\\n \u003ctextarea\\n value={text}\\n placeholder={'Chat to ' + contact.name}\\n onChange={e =\u003e setText(e.target.value)}\\n /\u003e\\n \u003cbr /\u003e\\n \u003cbutton\u003eSend to {contact.email}\u003c/button\u003e\\n \u003c/section\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-css\",\"children\":\".chat, .contact-list {\\n float: left;\\n margin-bottom: 20px;\\n}\\nul, li {\\n list-style: none;\\n margin: 0;\\n padding: 0;\\n}\\nli button {\\n width: 100px;\\n padding: 10px;\\n margin-right: 10px;\\n}\\ntextarea {\\n height: 150px;\\n}\\n\"}]}]]}],[\"$r\",\"MaxWidth\",\"58\",{\"children\":[\"\\n\",[\"$r\",\"LearnMore\",null,{\"path\":\"/learn/preserving-and-resetting-state\",\"children\":[\"$r\",\"p\",null,{\"children\":[\"Read \",[\"$r\",\"strong\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/preserving-and-resetting-state\",\"children\":\"Preserving and Resetting State\"}]}],\" to learn the lifetime of state and how to control it.\"]}]}],\"\\n\",[\"$r\",\"h2\",null,{\"id\":\"extracting-state-logic-into-a-reducer\",\"children\":\"Extracting state logic into a reducer \"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":\"Components with many state updates spread across many event handlers can get overwhelming. For these cases, you can consolidate all the state update logic outside your component in a single function, called “reducer”. Your event handlers become concise because they only specify the user “actions”. At the bottom of the file, the reducer function specifies how the state should update in response to each action!\"}],\"\\n\"]}],[\"$r\",\"Sandpack\",null,{\"children\":[[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/App.js\",\"children\":\"import { useReducer } from 'react';\\nimport AddTask from './AddTask.js';\\nimport TaskList from './TaskList.js';\\n\\nexport default function TaskApp() {\\n const [tasks, dispatch] = useReducer(\\n tasksReducer,\\n initialTasks\\n );\\n\\n function handleAddTask(text) {\\n dispatch({\\n type: 'added',\\n id: nextId++,\\n text: text,\\n });\\n }\\n\\n function handleChangeTask(task) {\\n dispatch({\\n type: 'changed',\\n task: task\\n });\\n }\\n\\n function handleDeleteTask(taskId) {\\n dispatch({\\n type: 'deleted',\\n id: taskId\\n });\\n }\\n\\n return (\\n \u003c\u003e\\n \u003ch1\u003ePrague itinerary\u003c/h1\u003e\\n \u003cAddTask\\n onAddTask={handleAddTask}\\n /\u003e\\n \u003cTaskList\\n tasks={tasks}\\n onChangeTask={handleChangeTask}\\n onDeleteTask={handleDeleteTask}\\n /\u003e\\n \u003c/\u003e\\n );\\n}\\n\\nfunction tasksReducer(tasks, action) {\\n switch (action.type) {\\n case 'added': {\\n return [...tasks, {\\n id: action.id,\\n text: action.text,\\n done: false\\n }];\\n }\\n case 'changed': {\\n return tasks.map(t =\u003e {\\n if (t.id === action.task.id) {\\n return action.task;\\n } else {\\n return t;\\n }\\n });\\n }\\n case 'deleted': {\\n return tasks.filter(t =\u003e t.id !== action.id);\\n }\\n default: {\\n throw Error('Unknown action: ' + action.type);\\n }\\n }\\n}\\n\\nlet nextId = 3;\\nconst initialTasks = [\\n { id: 0, text: 'Visit Kafka Museum', done: true },\\n { id: 1, text: 'Watch a puppet show', done: false },\\n { id: 2, text: 'Lennon Wall pic', done: false }\\n];\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/AddTask.js hidden\",\"children\":\"import { useState } from 'react';\\n\\nexport default function AddTask({ onAddTask }) {\\n const [text, setText] = useState('');\\n return (\\n \u003c\u003e\\n \u003cinput\\n placeholder=\\\"Add task\\\"\\n value={text}\\n onChange={e =\u003e setText(e.target.value)}\\n /\u003e\\n \u003cbutton onClick={() =\u003e {\\n setText('');\\n onAddTask(text);\\n }}\u003eAdd\u003c/button\u003e\\n \u003c/\u003e\\n )\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/TaskList.js hidden\",\"children\":\"import { useState } from 'react';\\n\\nexport default function TaskList({\\n tasks,\\n onChangeTask,\\n onDeleteTask\\n}) {\\n return (\\n \u003cul\u003e\\n {tasks.map(task =\u003e (\\n \u003cli key={task.id}\u003e\\n \u003cTask\\n task={task}\\n onChange={onChangeTask}\\n onDelete={onDeleteTask}\\n /\u003e\\n \u003c/li\u003e\\n ))}\\n \u003c/ul\u003e\\n );\\n}\\n\\nfunction Task({ task, onChange, onDelete }) {\\n const [isEditing, setIsEditing] = useState(false);\\n let taskContent;\\n if (isEditing) {\\n taskContent = (\\n \u003c\u003e\\n \u003cinput\\n value={task.text}\\n onChange={e =\u003e {\\n onChange({\\n ...task,\\n text: e.target.value\\n });\\n }} /\u003e\\n \u003cbutton onClick={() =\u003e setIsEditing(false)}\u003e\\n Save\\n \u003c/button\u003e\\n \u003c/\u003e\\n );\\n } else {\\n taskContent = (\\n \u003c\u003e\\n {task.text}\\n \u003cbutton onClick={() =\u003e setIsEditing(true)}\u003e\\n Edit\\n \u003c/button\u003e\\n \u003c/\u003e\\n );\\n }\\n return (\\n \u003clabel\u003e\\n \u003cinput\\n type=\\\"checkbox\\\"\\n checked={task.done}\\n onChange={e =\u003e {\\n onChange({\\n ...task,\\n done: e.target.checked\\n });\\n }}\\n /\u003e\\n {taskContent}\\n \u003cbutton onClick={() =\u003e onDelete(task.id)}\u003e\\n Delete\\n \u003c/button\u003e\\n \u003c/label\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-css\",\"children\":\"button { margin: 5px; }\\nli { list-style-type: none; }\\nul, li { margin: 0; padding: 0; }\\n\"}]}]]}],[\"$r\",\"MaxWidth\",\"68\",{\"children\":[\"\\n\",[\"$r\",\"LearnMore\",null,{\"path\":\"/learn/extracting-state-logic-into-a-reducer\",\"children\":[\"$r\",\"p\",null,{\"children\":[\"Read \",[\"$r\",\"strong\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/extracting-state-logic-into-a-reducer\",\"children\":\"Extracting State Logic into a Reducer\"}]}],\" to learn how to consolidate logic in the reducer function.\"]}]}],\"\\n\",[\"$r\",\"h2\",null,{\"id\":\"passing-data-deeply-with-context\",\"children\":\"Passing data deeply with context \"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":\"Usually, you will pass information from a parent component to a child component via props. But passing props can become inconvenient if you need to pass some prop through many components, or if many components need the same information. Context lets the parent component make some information available to any component in the tree below it—no matter how deep it is—without passing it explicitly through props.\"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":[\"Here, the \",[\"$r\",\"code\",null,{\"children\":\"Heading\"}],\" component determines its heading level by “asking” the closest \",[\"$r\",\"code\",null,{\"children\":\"Section\"}],\" for its level. Each \",[\"$r\",\"code\",null,{\"children\":\"Section\"}],\" tracks its own level by asking the parent \",[\"$r\",\"code\",null,{\"children\":\"Section\"}],\" and adding one to it. Every \",[\"$r\",\"code\",null,{\"children\":\"Section\"}],\" provides information to all components below it without passing props—it does that through context.\"]}],\"\\n\"]}],[\"$r\",\"Sandpack\",null,{\"children\":[[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"children\":\"import Heading from './Heading.js';\\nimport Section from './Section.js';\\n\\nexport default function Page() {\\n return (\\n \u003cSection\u003e\\n \u003cHeading\u003eTitle\u003c/Heading\u003e\\n \u003cSection\u003e\\n \u003cHeading\u003eHeading\u003c/Heading\u003e\\n \u003cHeading\u003eHeading\u003c/Heading\u003e\\n \u003cHeading\u003eHeading\u003c/Heading\u003e\\n \u003cSection\u003e\\n \u003cHeading\u003eSub-heading\u003c/Heading\u003e\\n \u003cHeading\u003eSub-heading\u003c/Heading\u003e\\n \u003cHeading\u003eSub-heading\u003c/Heading\u003e\\n \u003cSection\u003e\\n \u003cHeading\u003eSub-sub-heading\u003c/Heading\u003e\\n \u003cHeading\u003eSub-sub-heading\u003c/Heading\u003e\\n \u003cHeading\u003eSub-sub-heading\u003c/Heading\u003e\\n \u003c/Section\u003e\\n \u003c/Section\u003e\\n \u003c/Section\u003e\\n \u003c/Section\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/Section.js\",\"children\":\"import { useContext } from 'react';\\nimport { LevelContext } from './LevelContext.js';\\n\\nexport default function Section({ children }) {\\n const level = useContext(LevelContext);\\n return (\\n \u003csection className=\\\"section\\\"\u003e\\n \u003cLevelContext.Provider value={level + 1}\u003e\\n {children}\\n \u003c/LevelContext.Provider\u003e\\n \u003c/section\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/Heading.js\",\"children\":\"import { useContext } from 'react';\\nimport { LevelContext } from './LevelContext.js';\\n\\nexport default function Heading({ children }) {\\n const level = useContext(LevelContext);\\n switch (level) {\\n case 0:\\n throw Error('Heading must be inside a Section!');\\n case 1:\\n return \u003ch1\u003e{children}\u003c/h1\u003e;\\n case 2:\\n return \u003ch2\u003e{children}\u003c/h2\u003e;\\n case 3:\\n return \u003ch3\u003e{children}\u003c/h3\u003e;\\n case 4:\\n return \u003ch4\u003e{children}\u003c/h4\u003e;\\n case 5:\\n return \u003ch5\u003e{children}\u003c/h5\u003e;\\n case 6:\\n return \u003ch6\u003e{children}\u003c/h6\u003e;\\n default:\\n throw Error('Unknown level: ' + level);\\n }\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/LevelContext.js\",\"children\":\"import { createContext } from 'react';\\n\\nexport const LevelContext = createContext(0);\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-css\",\"children\":\".section {\\n padding: 10px;\\n margin: 5px;\\n border-radius: 5px;\\n border: 1px solid #aaa;\\n}\\n\"}]}]]}],[\"$r\",\"MaxWidth\",\"78\",{\"children\":[\"\\n\",[\"$r\",\"LearnMore\",null,{\"path\":\"/learn/passing-data-deeply-with-context\",\"children\":[\"$r\",\"p\",null,{\"children\":[\"Read \",[\"$r\",\"strong\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/passing-data-deeply-with-context\",\"children\":\"Passing Data Deeply with Context\"}]}],\" to learn about using context as an alternative to passing props.\"]}]}],\"\\n\",[\"$r\",\"h2\",null,{\"id\":\"scaling-up-with-reducer-and-context\",\"children\":\"Scaling up with reducer and context \"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":\"Reducers let you consolidate a component’s state update logic. Context lets you pass information deep down to other components. You can combine reducers and context together to manage state of a complex screen.\"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":\"With this approach, a parent component with complex state manages it with a reducer. Other components anywhere deep in the tree can read its state via context. They can also dispatch actions to update that state.\"}],\"\\n\"]}],[\"$r\",\"Sandpack\",null,{\"children\":[[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/App.js\",\"children\":\"import AddTask from './AddTask.js';\\nimport TaskList from './TaskList.js';\\nimport { TasksProvider } from './TasksContext.js';\\n\\nexport default function TaskApp() {\\n return (\\n \u003cTasksProvider\u003e\\n \u003ch1\u003eDay off in Kyoto\u003c/h1\u003e\\n \u003cAddTask /\u003e\\n \u003cTaskList /\u003e\\n \u003c/TasksProvider\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/TasksContext.js\",\"children\":\"import { createContext, useContext, useReducer } from 'react';\\n\\nconst TasksContext = createContext(null);\\nconst TasksDispatchContext = createContext(null);\\n\\nexport function TasksProvider({ children }) {\\n const [tasks, dispatch] = useReducer(\\n tasksReducer,\\n initialTasks\\n );\\n\\n return (\\n \u003cTasksContext.Provider value={tasks}\u003e\\n \u003cTasksDispatchContext.Provider\\n value={dispatch}\\n \u003e\\n {children}\\n \u003c/TasksDispatchContext.Provider\u003e\\n \u003c/TasksContext.Provider\u003e\\n );\\n}\\n\\nexport function useTasks() {\\n return useContext(TasksContext);\\n}\\n\\nexport function useTasksDispatch() {\\n return useContext(TasksDispatchContext);\\n}\\n\\nfunction tasksReducer(tasks, action) {\\n switch (action.type) {\\n case 'added': {\\n return [...tasks, {\\n id: action.id,\\n text: action.text,\\n done: false\\n }];\\n }\\n case 'changed': {\\n return tasks.map(t =\u003e {\\n if (t.id === action.task.id) {\\n return action.task;\\n } else {\\n return t;\\n }\\n });\\n }\\n case 'deleted': {\\n return tasks.filter(t =\u003e t.id !== action.id);\\n }\\n default: {\\n throw Error('Unknown action: ' + action.type);\\n }\\n }\\n}\\n\\nconst initialTasks = [\\n { id: 0, text: 'Philosopher’s Path', done: true },\\n { id: 1, text: 'Visit the temple', done: false },\\n { id: 2, text: 'Drink matcha', done: false }\\n];\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/AddTask.js\",\"children\":\"import { useState, useContext } from 'react';\\nimport { useTasksDispatch } from './TasksContext.js';\\n\\nexport default function AddTask({ onAddTask }) {\\n const [text, setText] = useState('');\\n const dispatch = useTasksDispatch();\\n return (\\n \u003c\u003e\\n \u003cinput\\n placeholder=\\\"Add task\\\"\\n value={text}\\n onChange={e =\u003e setText(e.target.value)}\\n /\u003e\\n \u003cbutton onClick={() =\u003e {\\n setText('');\\n dispatch({\\n type: 'added',\\n id: nextId++,\\n text: text,\\n });\\n }}\u003eAdd\u003c/button\u003e\\n \u003c/\u003e\\n );\\n}\\n\\nlet nextId = 3;\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-js\",\"meta\":\"src/TaskList.js\",\"children\":\"import { useState, useContext } from 'react';\\nimport { useTasks, useTasksDispatch } from './TasksContext.js';\\n\\nexport default function TaskList() {\\n const tasks = useTasks();\\n return (\\n \u003cul\u003e\\n {tasks.map(task =\u003e (\\n \u003cli key={task.id}\u003e\\n \u003cTask task={task} /\u003e\\n \u003c/li\u003e\\n ))}\\n \u003c/ul\u003e\\n );\\n}\\n\\nfunction Task({ task }) {\\n const [isEditing, setIsEditing] = useState(false);\\n const dispatch = useTasksDispatch();\\n let taskContent;\\n if (isEditing) {\\n taskContent = (\\n \u003c\u003e\\n \u003cinput\\n value={task.text}\\n onChange={e =\u003e {\\n dispatch({\\n type: 'changed',\\n task: {\\n ...task,\\n text: e.target.value\\n }\\n });\\n }} /\u003e\\n \u003cbutton onClick={() =\u003e setIsEditing(false)}\u003e\\n Save\\n \u003c/button\u003e\\n \u003c/\u003e\\n );\\n } else {\\n taskContent = (\\n \u003c\u003e\\n {task.text}\\n \u003cbutton onClick={() =\u003e setIsEditing(true)}\u003e\\n Edit\\n \u003c/button\u003e\\n \u003c/\u003e\\n );\\n }\\n return (\\n \u003clabel\u003e\\n \u003cinput\\n type=\\\"checkbox\\\"\\n checked={task.done}\\n onChange={e =\u003e {\\n dispatch({\\n type: 'changed',\\n task: {\\n ...task,\\n done: e.target.checked\\n }\\n });\\n }}\\n /\u003e\\n {taskContent}\\n \u003cbutton onClick={() =\u003e {\\n dispatch({\\n type: 'deleted',\\n id: task.id\\n });\\n }}\u003e\\n Delete\\n \u003c/button\u003e\\n \u003c/label\u003e\\n );\\n}\\n\"}]}],[\"$r\",\"pre\",null,{\"children\":[\"$r\",\"code\",null,{\"className\":\"language-css\",\"children\":\"button { margin: 5px; }\\nli { list-style-type: none; }\\nul, li { margin: 0; padding: 0; }\\n\"}]}]]}],[\"$r\",\"MaxWidth\",\"last\",{\"children\":[\"\\n\",[\"$r\",\"LearnMore\",null,{\"path\":\"/learn/scaling-up-with-reducer-and-context\",\"children\":[\"$r\",\"p\",null,{\"children\":[\"Read \",[\"$r\",\"strong\",null,{\"children\":[\"$r\",\"a\",null,{\"href\":\"/learn/scaling-up-with-reducer-and-context\",\"children\":\"Scaling Up with Reducer and Context\"}]}],\" to learn how state management scales in a growing app.\"]}]}],\"\\n\",[\"$r\",\"h2\",null,{\"id\":\"whats-next\",\"children\":\"What’s next? \"}],\"\\n\",[\"$r\",\"p\",null,{\"children\":[\"Head over to \",[\"$r\",\"a\",null,{\"href\":\"/learn/reacting-to-input-with-state\",\"children\":\"Reacting to Input with State\"}],\" to start reading this chapter page by page!\"]}],\"\\n\",[\"$r\",\"p\",null,{\"children\":[\"Or, if you’re already familiar with these topics, why not read about \",[\"$r\",\"a\",null,{\"href\":\"/learn/escape-hatches\",\"children\":\"Escape Hatches\"}],\"?\"]}]]}]]","meta":{"title":"Managing State"},"languages":null},"__N_SSG":true},"page":"/[[...markdownPath]]","query":{"markdownPath":["learn","managing-state"]},"buildId":"XJwnbMqphJWph8J-Ud_BN","isFallback":false,"gsp":true,"scriptLoader":[]}</script></body></html>