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class="document-toc-item "><a class="document-toc-link" href="#active_learning_printing_those_products">Active learning: Printing those products</a></li><li class="document-toc-item "><a class="document-toc-link" href="#active_learning_top_5_searches">Active learning: Top 5 searches</a></li><li class="document-toc-item "><a class="document-toc-link" href="#test_your_skills!">Test your skills!</a></li><li class="document-toc-item "><a class="document-toc-link" href="#conclusion">Conclusion</a></li><li class="document-toc-item "><a class="document-toc-link" href="#see_also">See also</a></li></ul></section></div></div><div class="sidebar-body"><ol><li class="section"><a href="/en-US/docs/Learn/Getting_started_with_the_web">Complete beginners start here!</a></li><li><details><summary>Getting started with the web</summary><ol><li><a href="/en-US/docs/Learn/Getting_started_with_the_web">Getting started with the web</a></li><li><a href="/en-US/docs/Learn/Getting_started_with_the_web/Installing_basic_software">Installing basic software</a></li><li><a href="/en-US/docs/Learn/Getting_started_with_the_web/What_will_your_website_look_like">What will your website look like?</a></li><li><a href="/en-US/docs/Learn/Getting_started_with_the_web/Dealing_with_files">Dealing with files</a></li><li><a href="/en-US/docs/Learn/Getting_started_with_the_web/HTML_basics">HTML basics</a></li><li><a href="/en-US/docs/Learn/Getting_started_with_the_web/CSS_basics">CSS basics</a></li><li><a href="/en-US/docs/Learn/Getting_started_with_the_web/JavaScript_basics">JavaScript basics</a></li><li><a href="/en-US/docs/Learn/Getting_started_with_the_web/Publishing_your_website">Publishing your website</a></li><li><a href="/en-US/docs/Learn/Getting_started_with_the_web/How_the_Web_works">How the web works</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/HTML">HTML — Structuring the web</a></li><li><details><summary>Introduction to HTML</summary><ol><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML">Introduction to HTML</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Getting_started">Getting started with HTML</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/The_head_metadata_in_HTML">What's in the head? Metadata in HTML</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/HTML_text_fundamentals">HTML text fundamentals</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Creating_hyperlinks">Creating hyperlinks</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Advanced_text_formatting">Advanced text formatting</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Document_and_website_structure">Document and website structure</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML">Debugging HTML</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Marking_up_a_letter">Marking up a letter</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Structuring_a_page_of_content">Structuring a page of content</a></li></ol></details></li><li><details><summary>Multimedia and embedding</summary><ol><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding">Multimedia and embedding</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Images_in_HTML">Images in HTML</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Video_and_audio_content">Video and audio content</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Other_embedding_technologies">From object to iframe — other embedding technologies</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Adding_vector_graphics_to_the_Web">Adding vector graphics to the web</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Responsive_images">Responsive images</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Mozilla_splash_page">Mozilla splash page</a></li></ol></details></li><li><details><summary>HTML tables</summary><ol><li><a href="/en-US/docs/Learn/HTML/Tables">HTML tables</a></li><li><a href="/en-US/docs/Learn/HTML/Tables/Basics">HTML table basics</a></li><li><a href="/en-US/docs/Learn/HTML/Tables/Advanced">HTML table advanced features and accessibility</a></li><li><a href="/en-US/docs/Learn/HTML/Tables/Structuring_planet_data">Structuring planet data</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/CSS">CSS — Styling the web</a></li><li><details><summary>CSS first steps</summary><ol><li><a href="/en-US/docs/Learn/CSS/First_steps">CSS first steps</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/What_is_CSS">What is CSS?</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/Getting_started">Getting started with CSS</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/How_CSS_is_structured">How CSS is structured</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/How_CSS_works">How CSS works</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/Styling_a_biography_page">Styling a biography page</a></li></ol></details></li><li><details><summary>CSS building blocks</summary><ol><li><a href="/en-US/docs/Learn/CSS/Building_blocks">CSS building blocks</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors">CSS selectors</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Type_Class_and_ID_Selectors">Type, class, and ID selectors</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Attribute_selectors">Attribute selectors</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Pseudo-classes_and_pseudo-elements">Pseudo-classes and pseudo-elements</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Combinators">Combinators</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Cascade_and_inheritance">Cascade, specificity, and inheritance</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Cascade_layers">Cascade layers</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/The_box_model">The box model</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Backgrounds_and_borders">Backgrounds and borders</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Handling_different_text_directions">Handling different text directions</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Overflowing_content">Overflowing content</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Values_and_units">CSS values and units</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Sizing_items_in_CSS">Sizing items in CSS</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Images_media_form_elements">Images, media, and form elements</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Styling_tables">Styling tables</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Advanced_styling_effects">Advanced styling effects</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Debugging_CSS">Debugging CSS</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Organizing">Organizing your CSS</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Fundamental_CSS_comprehension">Fundamental CSS comprehension</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Creating_fancy_letterheaded_paper">Creating fancy letterheaded paper</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/A_cool_looking_box">A cool-looking box</a></li></ol></details></li><li><details><summary>Styling text</summary><ol><li><a href="/en-US/docs/Learn/CSS/Styling_text">CSS styling text</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Fundamentals">Fundamental text and font styling</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Styling_lists">Styling lists</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Styling_links">Styling links</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Web_fonts">Web fonts</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Typesetting_a_homepage">Typesetting a community school homepage</a></li></ol></details></li><li><details><summary>CSS layout</summary><ol><li><a href="/en-US/docs/Learn/CSS/CSS_layout">CSS layout</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Introduction">Introduction to CSS layout</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Normal_Flow">Normal Flow</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Flexbox">Flexbox</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Grids">Grids</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Floats">Floats</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Positioning">Positioning</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Multiple-column_Layout">Multiple-column layout</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Responsive_Design">Responsive design</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Media_queries">Beginner's guide to media queries</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Legacy_Layout_Methods">Legacy layout methods</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Supporting_Older_Browsers">Supporting older browsers</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Fundamental_Layout_Comprehension">Fundamental layout comprehension</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/JavaScript">JavaScript — Dynamic client-side scripting</a></li><li><details open=""><summary>JavaScript first steps</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/First_steps">JavaScript first steps</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/What_is_JavaScript">What is JavaScript?</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/A_first_splash">A first splash into JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/What_went_wrong">What went wrong? Troubleshooting JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Variables">Storing the information you need — Variables</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Math">Basic math in JavaScript — numbers and operators</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Strings">Handling text — strings in JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods">Useful string methods</a></li><li><em><a href="/en-US/docs/Learn/JavaScript/First_steps/Arrays" aria-current="page">Arrays</a></em></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Silly_story_generator">Silly story generator</a></li></ol></details></li><li><details><summary>JavaScript building blocks</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks">JavaScript building blocks</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/conditionals">Making decisions in your code — conditionals</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Looping_code">Looping code</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Functions">Functions — reusable blocks of code</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Build_your_own_function">Build your own function</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Return_values">Function return values</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Events">Introduction to events</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Event_bubbling">Event bubbling</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Image_gallery">Image gallery</a></li></ol></details></li><li><details><summary>Introducing JavaScript objects</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Objects">Introducing JavaScript objects</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Basics">JavaScript object basics</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Object_prototypes">Object prototypes</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Object-oriented_programming">Object-oriented programming</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Classes_in_JavaScript">Classes in JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/JSON">Working with JSON</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Object_building_practice">Object building practice</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Adding_bouncing_balls_features">Adding features to our bouncing balls demo</a></li></ol></details></li><li><details><summary>Asynchronous JavaScript</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous">Asynchronous JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Introducing">Introducing asynchronous JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Promises">How to use promises</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Implementing_a_promise-based_API">How to implement a promise-based API</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Introducing_workers">Introducing workers</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Sequencing_animations">Sequencing animations</a></li></ol></details></li><li><details><summary>Client-side web APIs</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs">Client-side web APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Introduction">Introduction to web APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Manipulating_documents">Manipulating documents</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Fetching_data">Fetching data from the server</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Third_party_APIs">Third-party APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Drawing_graphics">Drawing graphics</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Video_and_audio_APIs">Video and Audio APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Client-side_storage">Client-side storage</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Forms">Web forms — Working with user data</a></li><li><details><summary>Web form building blocks</summary><ol><li><a href="/en-US/docs/Learn/Forms">Web form building blocks</a></li><li><a href="/en-US/docs/Learn/Forms/Your_first_form">Your first form</a></li><li><a href="/en-US/docs/Learn/Forms/How_to_structure_a_web_form">How to structure a web form</a></li><li><a href="/en-US/docs/Learn/Forms/Basic_native_form_controls">Basic native form controls</a></li><li><a href="/en-US/docs/Learn/Forms/HTML5_input_types">The HTML5 input types</a></li><li><a href="/en-US/docs/Learn/Forms/Other_form_controls">Other form controls</a></li><li><a href="/en-US/docs/Learn/Forms/Styling_web_forms">Styling web forms</a></li><li><a href="/en-US/docs/Learn/Forms/Advanced_form_styling">Advanced form styling</a></li><li><a href="/en-US/docs/Learn/Forms/UI_pseudo-classes">UI pseudo-classes</a></li><li><a href="/en-US/docs/Learn/Forms/Form_validation">Client-side form validation</a></li><li><a href="/en-US/docs/Learn/Forms/Sending_and_retrieving_form_data">Sending form data</a></li></ol></details></li><li><details><summary>Advanced web form techniques</summary><ol><li><a href="/en-US/docs/Learn/Forms/How_to_build_custom_form_controls">How to build custom form controls</a></li><li><a href="/en-US/docs/Learn/Forms/Sending_forms_through_JavaScript">Sending forms through JavaScript</a></li><li><a href="/en-US/docs/Learn/Forms/Property_compatibility_table_for_form_controls">CSS property compatibility table for form controls</a></li><li><a href="/en-US/docs/Learn/Forms/HTML_forms_in_legacy_browsers">HTML forms in legacy browsers</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Accessibility">Accessibility — Make the web usable by everyone</a></li><li><details><summary>Accessibility guides</summary><ol><li><a href="/en-US/docs/Learn/Accessibility">Accessibility</a></li><li><a href="/en-US/docs/Learn/Accessibility/What_is_accessibility">What is accessibility?</a></li><li><a href="/en-US/docs/Learn/Accessibility/HTML">HTML: A good basis for accessibility</a></li><li><a href="/en-US/docs/Learn/Accessibility/CSS_and_JavaScript">CSS and JavaScript accessibility best practices</a></li><li><a href="/en-US/docs/Learn/Accessibility/WAI-ARIA_basics">WAI-ARIA basics</a></li><li><a href="/en-US/docs/Learn/Accessibility/Multimedia">Accessible multimedia</a></li><li><a href="/en-US/docs/Learn/Accessibility/Mobile">Mobile accessibility</a></li><li><a href="/en-US/docs/Learn/Accessibility/Accessibility_troubleshooting">Assessment: Accessibility troubleshooting</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Performance">Performance — Making websites fast and responsive</a></li><li><details><summary>Performance guides</summary><ol><li><a href="/en-US/docs/Learn/Performance">Web performance</a></li><li><a href="/en-US/docs/Learn/Performance/why_web_performance">The "why" of web performance</a></li><li><a href="/en-US/docs/Learn/Performance/What_is_web_performance">What is web performance?</a></li><li><a href="/en-US/docs/Learn/Performance/Perceived_performance">Perceived performance</a></li><li><a href="/en-US/docs/Learn/Performance/Measuring_performance">Measuring performance</a></li><li><a href="/en-US/docs/Learn/Performance/Multimedia">Multimedia: Images</a></li><li><a href="/en-US/docs/Learn/Performance/video">Multimedia: video</a></li><li><a href="/en-US/docs/Learn/Performance/JavaScript">JavaScript performance optimization</a></li><li><a href="/en-US/docs/Learn/Performance/HTML">HTML performance optimization</a></li><li><a href="/en-US/docs/Learn/Performance/CSS">CSS performance optimization</a></li><li><a href="/en-US/docs/Learn/Performance/business_case_for_performance">The business case for web performance</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/MathML">MathML — Writing mathematics with MathML</a></li><li><details><summary>MathML first steps</summary><ol><li><a href="/en-US/docs/Learn/MathML/First_steps">MathML first steps</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Getting_started">Getting started with MathML</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Text_containers">MathML Text Containers</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Fractions_and_roots">MathML fractions and roots</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Scripts">MathML scripted elements</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Tables">MathML tables</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Three_famous_mathematical_formulas">Three famous mathematical formulas</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/../Games">Games — Developing games for the web</a></li><li><details><summary>Guides and tutorials</summary><ol><li><a href="/en-US/docs/Games/Introduction">Introduction to game development for the Web</a></li><li><a href="/en-US/docs/Games/Techniques">Techniques for game development</a></li><li><a href="/en-US/docs/Games/Tutorials">Tutorials</a></li><li><a href="/en-US/docs/Games/Publishing_games">Publishing games</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Tools_and_testing">Tools and testing</a></li><li><details><summary>Client-side web development tools</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools">Understanding client-side web development tools</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Overview">Client-side tooling overview</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Command_line">Command line crash course</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Package_management">Package management basics</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Introducing_complete_toolchain">Introducing a complete toolchain</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Deployment">Deploying our app</a></li></ol></details></li><li><details><summary>Introduction to client-side frameworks</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Introduction">Introduction to client-side frameworks</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Main_features">Framework main features</a></li></ol></details></li><li><details><summary>React</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_getting_started">Getting started with React</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_todo_list_beginning">Beginning our React todo list</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_components">Componentizing our React app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_events_state">React interactivity: Events and state</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_filtering_conditional_rendering">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_accessibility">Accessibility in React</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_resources">React resources</a></li></ol></details></li><li><details><summary>Ember</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_getting_started">Getting started with Ember</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_structure_componentization">Ember app structure and componentization</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_interactivity_events_state">Ember interactivity: Events, classes and state</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_conditional_footer">Ember Interactivity: Footer functionality, conditional rendering</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_routing">Routing in Ember</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_resources">Ember resources and troubleshooting</a></li></ol></details></li><li><details><summary>Vue</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_getting_started">Getting started with Vue</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_first_component">Creating our first Vue component</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_rendering_lists">Rendering a list of Vue components</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_methods_events_models">Adding a new todo form: Vue events, methods, and models</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_styling">Styling Vue components with CSS</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_computed_properties">Using Vue computed properties</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_conditional_rendering">Vue conditional rendering: editing existing todos</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_refs_focus_management">Vue refs and lifecycle methods for focus management</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_resources">Vue resources</a></li></ol></details></li><li><details><summary>Svelte</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_getting_started">Getting started with Svelte</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_Todo_list_beginning">Starting our Svelte to-do list app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_variables_props">Dynamic behavior in Svelte: working with variables and props</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_components">Componentizing our Svelte app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_reactivity_lifecycle_accessibility">Advanced Svelte: Reactivity, lifecycle, accessibility</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_stores">Working with Svelte stores</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_TypeScript">TypeScript support in Svelte</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_deployment_next">Deployment and next steps</a></li></ol></details></li><li><details><summary>Angular</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_getting_started">Getting started with Angular</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_todo_list_beginning">Beginning our Angular todo list app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_styling">Styling our Angular app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_item_component">Creating an item component</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_filtering">Filtering our to-do items</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_building">Building Angular applications and further resources</a></li></ol></details></li><li><details><summary>Git and GitHub</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/GitHub">Git and GitHub</a></li></ol></details></li><li><details><summary>Cross browser testing</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing">Cross browser testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Introduction">Introduction to cross-browser testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Testing_strategies">Strategies for carrying out testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/HTML_and_CSS">Handling common HTML and CSS problems</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/JavaScript">Handling common JavaScript problems</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Accessibility">Handling common accessibility problems</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Feature_detection">Implementing feature detection</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Automated_testing">Introduction to automated testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Your_own_automation_environment">Setting up your own test automation environment</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Server-side">Server-side website programming</a></li><li><details><summary>First steps</summary><ol><li><a href="/en-US/docs/Learn/Server-side/First_steps">Server-side website programming first steps</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Introduction">Introduction to the server side</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Client-Server_overview">Client-Server Overview</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Web_frameworks">Server-side web frameworks</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Website_security">Website security</a></li></ol></details></li><li><details><summary>Django web framework (Python)</summary><ol><li><a href="/en-US/docs/Learn/Server-side/Django">Django Web Framework (Python)</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Introduction">Django introduction</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/development_environment">Setting up a Django development environment</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Tutorial_local_library_website">Django Tutorial: The Local Library website</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/skeleton_website">Django Tutorial Part 2: Creating a skeleton website</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Models">Django Tutorial Part 3: Using models</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Admin_site">Django Tutorial Part 4: Django admin site</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Home_page">Django Tutorial Part 5: Creating our home page</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Generic_views">Django Tutorial Part 6: Generic list and detail views</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Sessions">Django Tutorial Part 7: Sessions framework</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Authentication">Django Tutorial Part 8: User authentication and permissions</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Forms">Django Tutorial Part 9: Working with forms</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Testing">Django Tutorial Part 10: Testing a Django web application</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Deployment">Django Tutorial Part 11: Deploying Django to production</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/web_application_security">Django web application security</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/django_assessment_blog">Assessment: DIY Django mini blog</a></li></ol></details></li><li><details><summary>Express Web Framework (Node.js/JavaScript)</summary><ol><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs">Express web framework (Node.js/JavaScript)</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/Introduction">Express/Node introduction</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/development_environment">Setting up a Node development environment</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/Tutorial_local_library_website">Express Tutorial: The Local Library website</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/skeleton_website">Express Tutorial Part 2: Creating a skeleton website</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/mongoose">Express Tutorial Part 3: Using a Database (with Mongoose)</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/routes">Express Tutorial Part 4: Routes and controllers</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/Displaying_data">Express Tutorial Part 5: Displaying library data</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/forms">Express Tutorial Part 6: Working with forms</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/deployment">Express Tutorial Part 7: Deploying to production</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Common_questions">Further resources</a></li><li><details><summary>Common questions</summary><ol><li><a href="/en-US/docs/Learn/Common_questions">Common questions</a></li><li><a href="/en-US/docs/Learn/HTML/Howto">Use HTML to solve common problems</a></li><li><a href="/en-US/docs/Learn/CSS/Howto">Use CSS to solve common problems</a></li><li><a href="/en-US/docs/Learn/JavaScript/Howto">Solve common problems in your JavaScript code</a></li><li><a href="/en-US/docs/Learn/Common_questions/Web_mechanics">Web mechanics</a></li><li><a href="/en-US/docs/Learn/Common_questions/Tools_and_setup">Tools and setup</a></li><li><a href="/en-US/docs/Learn/Common_questions/Design_and_accessibility">Design and accessibility</a></li></ol></details></li></ol></div></div><section class="place side"></section></nav></aside><div class="toc-container"><aside class="toc"><nav><div class="document-toc-container"><section class="document-toc"><header><h2 class="document-toc-heading">In this article</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#what_is_an_array">What is an array?</a></li><li class="document-toc-item "><a class="document-toc-link" href="#creating_arrays">Creating arrays</a></li><li class="document-toc-item "><a class="document-toc-link" href="#finding_the_length_of_an_array">Finding the length of an array</a></li><li class="document-toc-item "><a class="document-toc-link" href="#accessing_and_modifying_array_items">Accessing and modifying array items</a></li><li class="document-toc-item "><a class="document-toc-link" href="#finding_the_index_of_items_in_an_array">Finding the index of items in an array</a></li><li class="document-toc-item "><a class="document-toc-link" href="#adding_items">Adding items</a></li><li class="document-toc-item "><a class="document-toc-link" href="#removing_items">Removing items</a></li><li class="document-toc-item "><a class="document-toc-link" href="#accessing_every_item">Accessing every item</a></li><li class="document-toc-item "><a class="document-toc-link" href="#converting_between_strings_and_arrays">Converting between strings and arrays</a></li><li class="document-toc-item "><a class="document-toc-link" href="#active_learning_printing_those_products">Active learning: Printing those products</a></li><li class="document-toc-item "><a class="document-toc-link" href="#active_learning_top_5_searches">Active learning: Top 5 searches</a></li><li class="document-toc-item "><a class="document-toc-link" href="#test_your_skills!">Test your skills!</a></li><li class="document-toc-item "><a class="document-toc-link" href="#conclusion">Conclusion</a></li><li class="document-toc-item "><a class="document-toc-link" href="#see_also">See also</a></li></ul></section></div></nav></aside><section class="place side"></section></div></div><main id="content" class="main-content "><article class="main-page-content" lang="en-US"><header><h1>Arrays</h1></header><div class="section-content"><ul class="prev-next"> <li><a class="button secondary" href="/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods"><span class="button-wrap"> Previous </span></a></li> <li><a class="button secondary" href="/en-US/docs/Learn/JavaScript/First_steps"><span class="button-wrap"> Overview: JavaScript first steps</span></a></li> <li><a class="button secondary" href="/en-US/docs/Learn/JavaScript/First_steps/Silly_story_generator"><span class="button-wrap"> Next </span></a></li> </ul> <p>In the final article of this module, we'll look at arrays — a neat way of storing a list of data items under a single variable name. Here we look at why this is useful, then explore how to create an array, retrieve, add, and remove items stored in an array, and more besides.</p> <figure class="table-container"><table> <tbody> <tr> <th scope="row">Prerequisites:</th> <td> A basic understanding of HTML and CSS, an understanding of what JavaScript is. </td> </tr> <tr> <th scope="row">Objective:</th> <td>To understand what arrays are and how to manipulate them in JavaScript.</td> </tr> </tbody> </table></figure></div><section aria-labelledby="what_is_an_array"><h2 id="what_is_an_array"><a href="#what_is_an_array">What is an array?</a></h2><div class="section-content"><p>Arrays are generally described as "list-like objects"; they are basically single objects that contain multiple values stored in a list. Array objects can be stored in variables and dealt with in much the same way as any other type of value, the difference being that we can access each value inside the list individually, and do super useful and efficient things with the list, like loop through it and do the same thing to every value. Maybe we've got a series of product items and their prices stored in an array, and we want to loop through them all and print them out on an invoice, while totaling all the prices together and printing out the total price at the bottom.</p> <p>If we didn't have arrays, we'd have to store every item in a separate variable, then call the code that does the printing and adding separately for each item. This would be much longer to write out, less efficient, and more error-prone. If we had 10 items to add to the invoice it would already be annoying, but what about 100 items, or 1000? We'll return to this example later on in the article.</p> <p>As in previous articles, let's learn about the real basics of arrays by entering some examples into <a href="/en-US/docs/Learn/Common_questions/Tools_and_setup/What_are_browser_developer_tools">browser developer console</a>.</p></div></section><section aria-labelledby="creating_arrays"><h2 id="creating_arrays"><a href="#creating_arrays">Creating arrays</a></h2><div class="section-content"><p>Arrays consist of square brackets and items that are separated by commas.</p> <ol> <li> <p>Suppose we want to store a shopping list in an array. Paste the following code into the console:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const shopping = ["bread", "milk", "cheese", "hummus", "noodles"]; console.log(shopping); </code></pre></div> </li> <li> <p>In the above example, each item is a string, but in an array we can store various data types — strings, numbers, objects, and even other arrays. We can also mix data types in a single array — we do not have to limit ourselves to storing only numbers in one array, and in another only strings. For example:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const sequence = [1, 1, 2, 3, 5, 8, 13]; const random = ["tree", 795, [0, 1, 2]]; </code></pre></div> </li> <li> <p>Before proceeding, create a few example arrays.</p> </li> </ol></div></section><section aria-labelledby="finding_the_length_of_an_array"><h2 id="finding_the_length_of_an_array"><a href="#finding_the_length_of_an_array">Finding the length of an array</a></h2><div class="section-content"><p>You can find out the length of an array (how many items are in it) in exactly the same way as you find out the length (in characters) of a string — by using the <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/length"><code>length</code></a> property. Try the following:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const shopping = ["bread", "milk", "cheese", "hummus", "noodles"]; console.log(shopping.length); // 5 </code></pre></div></div></section><section aria-labelledby="accessing_and_modifying_array_items"><h2 id="accessing_and_modifying_array_items"><a href="#accessing_and_modifying_array_items">Accessing and modifying array items</a></h2><div class="section-content"><p>Items in an array are numbered, starting from zero. This number is called the item's <em>index</em>. So the first item has index 0, the second has index 1, and so on. You can access individual items in the array using bracket notation and supplying the item's index, in the same way that you <a href="/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods#retrieving_a_specific_string_character">accessed the letters in a string</a>.</p> <ol> <li> <p>Enter the following into your console:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const shopping = ["bread", "milk", "cheese", "hummus", "noodles"]; console.log(shopping[0]); // returns "bread" </code></pre></div> </li> <li> <p>You can also modify an item in an array by giving a single array item a new value. Try this:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const shopping = ["bread", "milk", "cheese", "hummus", "noodles"]; shopping[0] = "tahini"; console.log(shopping); // shopping will now return [ "tahini", "milk", "cheese", "hummus", "noodles" ] </code></pre></div> <div class="notecard note"> <p><strong>Note:</strong> We've said it before, but just as a reminder — JavaScript starts indexing arrays at zero!</p> </div> </li> <li> <p>Note that an array inside an array is called a multidimensional array. You can access an item inside an array that is itself inside another array by chaining two sets of square brackets together. For example, to access one of the items inside the array that is the third item inside the <code>random</code> array (see previous section), we could do something like this:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const random = ["tree", 795, [0, 1, 2]]; random[2][2]; </code></pre></div> </li> <li> <p>Try making some more modifications to your array examples before moving on. Play around a bit, and see what works and what doesn't.</p> </li> </ol></div></section><section aria-labelledby="finding_the_index_of_items_in_an_array"><h2 id="finding_the_index_of_items_in_an_array"><a href="#finding_the_index_of_items_in_an_array">Finding the index of items in an array</a></h2><div class="section-content"><p> If you don't know the index of an item, you can use the <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf"><code>indexOf()</code></a> method. The <code>indexOf()</code> method takes an item as an argument and will either return the item's index or <code>-1</code> if the item is not in the array: </p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const birds = ["Parrot", "Falcon", "Owl"]; console.log(birds.indexOf("Owl")); // 2 console.log(birds.indexOf("Rabbit")); // -1 </code></pre></div></div></section><section aria-labelledby="adding_items"><h2 id="adding_items"><a href="#adding_items">Adding items</a></h2><div class="section-content"><p>To add one or more items to the end of an array we can use <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push"><code>push()</code></a>. Note that you need to include one or more items that you want to add to the end of your array.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const cities = ["Manchester", "Liverpool"]; cities.push("Cardiff"); console.log(cities); // [ "Manchester", "Liverpool", "Cardiff" ] cities.push("Bradford", "Brighton"); console.log(cities); // [ "Manchester", "Liverpool", "Cardiff", "Bradford", "Brighton" ] </code></pre></div> <p>The new length of the array is returned when the method call completes. If you wanted to store the new array length in a variable, you could do something like this:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const cities = ["Manchester", "Liverpool"]; const newLength = cities.push("Bristol"); console.log(cities); // [ "Manchester", "Liverpool", "Bristol" ] console.log(newLength); // 3 </code></pre></div> <p>To add an item to the start of the array, use <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/unshift"><code>unshift()</code></a>:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const cities = ["Manchester", "Liverpool"]; cities.unshift("Edinburgh"); console.log(cities); // [ "Edinburgh", "Manchester", "Liverpool" ] </code></pre></div></div></section><section aria-labelledby="removing_items"><h2 id="removing_items"><a href="#removing_items">Removing items</a></h2><div class="section-content"><p>To remove the last item from the array, use <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/pop"><code>pop()</code></a>.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const cities = ["Manchester", "Liverpool"]; cities.pop(); console.log(cities); // [ "Manchester" ] </code></pre></div> <p>The <code>pop()</code> method returns the item that was removed. To save that item in a new variable, you could do this:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const cities = ["Manchester", "Liverpool"]; const removedCity = cities.pop(); console.log(removedCity); // "Liverpool" </code></pre></div> <p>To remove the first item from an array, use <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/shift"><code>shift()</code></a>:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const cities = ["Manchester", "Liverpool"]; cities.shift(); console.log(cities); // [ "Liverpool" ] </code></pre></div> <p>If you know the index of an item, you can remove it from the array using <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice"><code>splice()</code></a>:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const cities = ["Manchester", "Liverpool", "Edinburgh", "Carlisle"]; const index = cities.indexOf("Liverpool"); if (index !== -1) { cities.splice(index, 1); } console.log(cities); // [ "Manchester", "Edinburgh", "Carlisle" ] </code></pre></div> <p>In this call to <code>splice()</code>, the first argument says where to start removing items, and the second argument says how many items should be removed. So you can remove more than one item:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const cities = ["Manchester", "Liverpool", "Edinburgh", "Carlisle"]; const index = cities.indexOf("Liverpool"); if (index !== -1) { cities.splice(index, 2); } console.log(cities); // [ "Manchester", "Carlisle" ] </code></pre></div></div></section><section aria-labelledby="accessing_every_item"><h2 id="accessing_every_item"><a href="#accessing_every_item">Accessing every item</a></h2><div class="section-content"><p>Very often you will want to access every item in the array. You can do this using the <a href="/en-US/docs/Web/JavaScript/Reference/Statements/for...of"><code>for...of</code></a> statement:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const birds = ["Parrot", "Falcon", "Owl"]; for (const bird of birds) { console.log(bird); } </code></pre></div> <p>Sometimes you will want to do the same thing to each item in an array, leaving you with an array containing the changed items. You can do this using <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map"><code>map()</code></a>. The code below takes an array of numbers and doubles each number:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function double(number) { return number * 2; } const numbers = [5, 2, 7, 6]; const doubled = numbers.map(double); console.log(doubled); // [ 10, 4, 14, 12 ] </code></pre></div> <p>We give a function to the <code>map()</code>, and <code>map()</code> calls the function once for each item in the array, passing in the item. It then adds the return value from each function call to a new array, and finally returns the new array.</p> <p>Sometimes you'll want to create a new array containing only the items in the original array that match some test. You can do that using <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter"><code>filter()</code></a>. The code below takes an array of strings and returns an array containing just the strings that are greater than 8 characters long:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function isLong(city) { return city.length > 8; } const cities = ["London", "Liverpool", "Totnes", "Edinburgh"]; const longer = cities.filter(isLong); console.log(longer); // [ "Liverpool", "Edinburgh" ] </code></pre></div> <p>Like <code>map()</code>, we give a function to the <code>filter()</code> method, and <code>filter()</code> calls this function for every item in the array, passing in the item. If the function returns <code>true</code>, then the item is added to a new array. Finally it returns the new array.</p></div></section><section aria-labelledby="converting_between_strings_and_arrays"><h2 id="converting_between_strings_and_arrays"><a href="#converting_between_strings_and_arrays">Converting between strings and arrays</a></h2><div class="section-content"><p>Often you'll be presented with some raw data contained in a big long string, and you might want to separate the useful items out into a more useful form and then do things to them, like display them in a data table. To do this, we can use the <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split"><code>split()</code></a> method. In its simplest form, this takes a single parameter, the character you want to separate the string at, and returns the substrings between the separator as items in an array.</p> <div class="notecard note"> <p><strong>Note:</strong> Okay, this is technically a string method, not an array method, but we've put it in with arrays as it goes well here.</p> </div> <ol> <li> <p>Let's play with this, to see how it works. First, create a string in your console:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const data = "Manchester,London,Liverpool,Birmingham,Leeds,Carlisle"; </code></pre></div> </li> <li> <p>Now let's split it at each comma:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const cities = data.split(","); cities; </code></pre></div> </li> <li> <p>Finally, try finding the length of your new array, and retrieving some items from it:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>cities.length; cities[0]; // the first item in the array cities[1]; // the second item in the array cities[cities.length - 1]; // the last item in the array </code></pre></div> </li> <li> <p>You can also go the opposite way using the <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join"><code>join()</code></a> method. Try the following:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const commaSeparated = cities.join(","); commaSeparated; </code></pre></div> </li> <li> <p>Another way of converting an array to a string is to use the <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toString"><code>toString()</code></a> method. <code>toString()</code> is arguably simpler than <code>join()</code> as it doesn't take a parameter, but more limiting. With <code>join()</code> you can specify different separators, whereas <code>toString()</code> always uses a comma. (Try running Step 4 with a different character than a comma.)</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const dogNames = ["Rocket", "Flash", "Bella", "Slugger"]; dogNames.toString(); // Rocket,Flash,Bella,Slugger </code></pre></div> </li> </ol></div></section><section aria-labelledby="active_learning_printing_those_products"><h2 id="active_learning_printing_those_products"><a href="#active_learning_printing_those_products">Active learning: Printing those products</a></h2><div class="section-content"><p>Let's return to the example we described earlier — printing out product names and prices on an invoice, then totaling the prices and printing them at the bottom. In the editable example below there are comments containing numbers — each of these marks a place where you have to add something to the code. They are as follows:</p> <ol> <li>Below the <code>// number 1</code> comment are a number of strings, each one containing a product name and price separated by a colon. We'd like you to turn this into an array and store it in an array called <code>products</code>.</li> <li>Below the <code>// number 2</code> comment, start a <code>for...of()</code> loop to go through every item in the <code>products</code> array.</li> <li>Below the <code>// number 3</code> comment we want you to write a line of code that splits the current array item (<code>name:price</code>) into two separate items, one containing just the name and one containing just the price. If you are not sure how to do this, consult the <a href="/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods">Useful string methods</a> article for some help, or even better, look at the <a href="#converting_between_strings_and_arrays">Converting between strings and arrays</a> section of this article.</li> <li>As part of the above line of code, you'll also want to convert the price from a string to a number. If you can't remember how to do this, check out the <a href="/en-US/docs/Learn/JavaScript/First_steps/Strings#numbers_vs._strings">first strings article</a>.</li> <li>There is a variable called <code>total</code> that is created and given a value of 0 at the top of the code. Inside the loop (below <code>// number 4</code>) we want you to add a line that adds the current item price to that total in each iteration of the loop, so that at the end of the code the correct total is printed onto the invoice. You might need an <a href="/en-US/docs/Learn/JavaScript/First_steps/Math#assignment_operators">assignment operator</a> to do this.</li> <li>We want you to change the line just below <code>// number 5</code> so that the <code>itemText</code> variable is made equal to "current item name — $current item price", for example "Shoes — $23.99" in each case, so the correct information for each item is printed on the invoice. This is just simple string concatenation, which should be familiar to you.</li> <li>Finally, below the <code>// number 6</code> comment, you'll need to add a <code>}</code> to mark the end of the <code>for...of()</code> loop.</li> </ol> <div class="code-example"><pre class="brush: html hidden notranslate"><code><h2>Live output</h2> <div class="output" style="min-height: 150px;"> <ul></ul> <p></p> </div> <h2>Editable code</h2> <p class="a11y-label"> Press Esc to move focus away from the code area (Tab inserts a tab character). </p> <textarea id="code" class="playable-code" style="height: 410px;width: 95%"> const list = document.querySelector('.output ul'); const totalBox = document.querySelector('.output p'); let total = 0; list.textContent = ""; totalBox.textContent = ""; // number 1 'Underpants:6.99' 'Socks:5.99' 'T-shirt:14.99' 'Trousers:31.99' 'Shoes:23.99'; // number 2 // number 3 // number 4 // number 5 let itemText = 0; const listItem = document.createElement('li'); listItem.textContent = itemText; list.appendChild(listItem); // number 6 totalBox.textContent = 'Total: $' + total.toFixed(2); </textarea> <div class="playable-buttons"> <input id="reset" type="button" value="Reset" /> <input id="solution" type="button" value="Show solution" /> </div> </code></pre></div> <div class="code-example"><pre class="brush: js hidden notranslate"><code>const textarea = document.getElementById("code"); const reset = document.getElementById("reset"); const solution = document.getElementById("solution"); let code = textarea.value; let userEntry = textarea.value; function updateCode() { eval(textarea.value); } reset.addEventListener("click", () => { textarea.value = code; userEntry = textarea.value; solutionEntry = jsSolution; solution.value = "Show solution"; updateCode(); }); solution.addEventListener("click", () => { if (solution.value === "Show solution") { textarea.value = solutionEntry; solution.value = "Hide solution"; } else { textarea.value = userEntry; solution.value = "Show solution"; } updateCode(); }); const jsSolution = `const list = document.querySelector('.output ul'); const totalBox = document.querySelector('.output p'); let total = 0; list.textContent = ""; totalBox.textContent = ""; const products = [ 'Underpants:6.99', 'Socks:5.99', 'T-shirt:14.99', 'Trousers:31.99', 'Shoes:23.99', ]; for (const product of products) { const subArray = product.split(':'); const name = subArray[0]; const price = Number(subArray[1]); total += price; const itemText = \`\${name} — $\${price}\`; const listItem = document.createElement('li'); listItem.textContent = itemText; list.appendChild(listItem); } totalBox.textContent = \`Total: $\${total.toFixed(2)}\`;`; let solutionEntry = jsSolution; textarea.addEventListener("input", updateCode); window.addEventListener("load", updateCode); // stop tab key tabbing out of textarea and // make it write a tab at the caret position instead textarea.onkeydown = (event) => { if (event.code === "Tab") { event.preventDefault(); insertAtCaret("\t"); } if (event.code === "Escape") { textarea.blur(); } }; function insertAtCaret(text) { const scrollPos = textarea.scrollTop; let caretPos = textarea.selectionStart; const front = textarea.value.substring(0, caretPos); const back = textarea.value.substring( textarea.selectionEnd, textarea.value.length, ); textarea.value = front + text + back; caretPos += text.length; textarea.selectionStart = caretPos; textarea.selectionEnd = caretPos; textarea.focus(); textarea.scrollTop = scrollPos; } // Update the saved userCode every time the user updates the text area code textarea.onkeyup = () => { // We only want to save the state when the user code is being shown, // not the solution, so that solution is not saved over the user code if (solution.value === "Show solution") { userEntry = textarea.value; } else { solutionEntry = textarea.value; } updateCode(); }; </code></pre></div> <div class="code-example"><pre class="brush: css hidden notranslate"><code>html { font-family: sans-serif; } h2 { font-size: 16px; } .a11y-label { margin: 0; text-align: right; font-size: 0.7rem; width: 98%; } body { margin: 10px; background-color: #f5f9fa; } </code></pre></div><div class="code-example"><div class="example-header"></div><iframe class="sample-code-frame" title="Active learning Printing those products sample" id="frame_active_learning_printing_those_products" width="100%" height="750" src="about:blank" data-live-path="/en-US/docs/Learn/JavaScript/First_steps/Arrays" data-live-id="active_learning_printing_those_products" sandbox="allow-same-origin allow-scripts" loading="lazy"></iframe></div></div></section><section aria-labelledby="active_learning_top_5_searches"><h2 id="active_learning_top_5_searches"><a href="#active_learning_top_5_searches">Active learning: Top 5 searches</a></h2><div class="section-content"><p>A good use for array methods like <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push"><code>push()</code></a> and <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/pop"><code>pop()</code></a> is when you are maintaining a record of currently active items in a web app. In an animated scene for example, you might have an array of objects representing the background graphics currently displayed, and you might only want 50 displayed at once, for performance or clutter reasons. As new objects are created and added to the array, older ones can be deleted from the array to maintain the desired number.</p> <p>In this example we're going to show a much simpler use — here we're giving you a fake search site, with a search box. The idea is that when terms are entered in the search box, the top 5 previous search terms are displayed in the list. When the number of terms goes over 5, the last term starts being deleted each time a new term is added to the top, so the 5 previous terms are always displayed.</p> <div class="notecard note"> <p><strong>Note:</strong> In a real search app, you'd probably be able to click the previous search terms to return to previous searches, and it would display actual search results! We are just keeping it simple for now.</p> </div> <p>To complete the app, we need you to:</p> <ol> <li>Add a line below the <code>// number 1</code> comment that adds the current value entered into the search input to the start of the array. This can be retrieved using <code>searchInput.value</code>.</li> <li>Add a line below the <code>// number 2</code> comment that removes the value currently at the end of the array.</li> </ol> <div class="code-example"><pre class="brush: html hidden notranslate"><code><h2>Live output</h2> <div class="output" style="min-height: 150px;"> <input type="text" /><button>Search</button> <ul></ul> </div> <h2>Editable code</h2> <p class="a11y-label"> Press Esc to move focus away from the code area (Tab inserts a tab character). </p> <textarea id="code" class="playable-code" style="height: 370px; width: 95%"> const list = document.querySelector('.output ul'); const searchInput = document.querySelector('.output input'); const searchBtn = document.querySelector('.output button'); list.textContent = ""; const myHistory = []; const MAX_HISTORY = 5; searchBtn.onclick = () => { // we will only allow a term to be entered if the search input isn't empty if (searchInput.value !== '') { // number 1 // empty the list so that we don't display duplicate entries // the display is regenerated every time a search term is entered. list.textContent = ""; // loop through the array, and display all the search terms in the list for (const itemText of myHistory) { const listItem = document.createElement('li'); listItem.textContent = itemText; list.appendChild(listItem); } // If the array length is 5 or more, remove the oldest search term if (myHistory.length >= MAX_HISTORY) { // number 2 } // empty the search input and focus it, ready for the next term to be entered searchInput.value = ''; searchInput.focus(); } } </textarea> <div class="playable-buttons"> <input id="reset" type="button" value="Reset" /> <input id="solution" type="button" value="Show solution" /> </div> </code></pre></div> <div class="code-example"><pre class="brush: css hidden notranslate"><code>html { font-family: sans-serif; } h2 { font-size: 16px; } .a11y-label { margin: 0; text-align: right; font-size: 0.7rem; width: 98%; } body { margin: 10px; background: #f5f9fa; } </code></pre></div> <div class="code-example"><pre class="brush: js hidden notranslate"><code>const textarea = document.getElementById("code"); const reset = document.getElementById("reset"); const solution = document.getElementById("solution"); let code = textarea.value; let userEntry = textarea.value; function updateCode() { eval(textarea.value); } reset.addEventListener("click", () => { textarea.value = code; userEntry = textarea.value; solutionEntry = jsSolution; solution.value = "Show solution"; updateCode(); }); solution.addEventListener("click", () => { if (solution.value === "Show solution") { textarea.value = solutionEntry; solution.value = "Hide solution"; } else { textarea.value = userEntry; solution.value = "Show solution"; } updateCode(); }); const jsSolution = `const list = document.querySelector('.output ul'); const searchInput = document.querySelector('.output input'); const searchBtn = document.querySelector('.output button'); list.textContent = ""; const myHistory = []; const MAX_HISTORY = 5; searchBtn.onclick = () => { // we will only allow a term to be entered if the search input isn't empty if (searchInput.value !== '') { myHistory.unshift(searchInput.value); // empty the list so that we don't display duplicate entries // the display is regenerated every time a search term is entered. list.textContent = ""; // loop through the array, and display all the search terms in the list for (const itemText of myHistory) { const listItem = document.createElement('li'); listItem.textContent = itemText; list.appendChild(listItem); } // If the array length is 5 or more, remove the oldest search term if (myHistory.length >= MAX_HISTORY) { myHistory.pop(); } // empty the search input and focus it, ready for the next term to be entered searchInput.value = ''; searchInput.focus(); } }`; let solutionEntry = jsSolution; textarea.addEventListener("input", updateCode); window.addEventListener("load", updateCode); // stop tab key tabbing out of textarea and // make it write a tab at the caret position instead textarea.onkeydown = (event) => { if (event.code === "Tab") { event.preventDefault(); insertAtCaret("\t"); } if (event.code === "Escape") { textarea.blur(); } }; function insertAtCaret(text) { const scrollPos = textarea.scrollTop; let caretPos = textarea.selectionStart; const front = textarea.value.substring(0, caretPos); const back = textarea.value.substring( textarea.selectionEnd, textarea.value.length, ); textarea.value = front + text + back; caretPos += text.length; textarea.selectionStart = caretPos; textarea.selectionEnd = caretPos; textarea.focus(); textarea.scrollTop = scrollPos; } // Update the saved userCode every time the user updates the text area code textarea.onkeyup = () => { // We only want to save the state when the user code is being shown, // not the solution, so that solution is not saved over the user code if (solution.value === "Show solution") { userEntry = textarea.value; } else { solutionEntry = textarea.value; } updateCode(); }; </code></pre></div><div class="code-example"><div class="example-header"></div><iframe class="sample-code-frame" title="Active learning Top 5 searches sample" id="frame_active_learning_top_5_searches" width="100%" height="700" src="about:blank" data-live-path="/en-US/docs/Learn/JavaScript/First_steps/Arrays" data-live-id="active_learning_top_5_searches" sandbox="allow-same-origin allow-scripts" loading="lazy"></iframe></div></div></section><section aria-labelledby="test_your_skills!"><h2 id="test_your_skills!"><a href="#test_your_skills!">Test your skills!</a></h2><div class="section-content"><p>You've reached the end of this article, but can you remember the most important information? You can find some further tests to verify that you've retained this information before you move on — see <a href="/en-US/docs/Learn/JavaScript/First_steps/Test_your_skills:_Arrays">Test your skills: Arrays</a>.</p></div></section><section aria-labelledby="conclusion"><h2 id="conclusion"><a href="#conclusion">Conclusion</a></h2><div class="section-content"><p>After reading through this article, we are sure you will agree that arrays seem pretty darn useful; you'll see them crop up everywhere in JavaScript, often in association with loops in order to do the same thing to every item in an array. We'll be teaching you all the useful basics there are to know about loops in the next module, but for now you should give yourself a clap and take a well-deserved break; you've worked through all the articles in this module!</p> <p>The only thing left to do is work through this module's assessment, which will test your understanding of the articles that came before it.</p></div></section><section aria-labelledby="see_also"><h2 id="see_also"><a href="#see_also">See also</a></h2><div class="section-content"><ul> <li><a href="/en-US/docs/Web/JavaScript/Guide/Indexed_collections">Indexed collections</a> — an advanced level guide to arrays and their cousins, typed arrays.</li> <li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array"><code>Array</code></a> — the <code>Array</code> object reference page — for a detailed reference guide to the features discussed in this page, and many more.</li> </ul><ul class="prev-next"> <li><a class="button secondary" 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Content available under <a href="/en-US/docs/MDN/Writing_guidelines/Attrib_copyright_license">a Creative Commons license</a>.</p></div></div></footer></div><script type="application/json" id="hydration">{"url":"/en-US/docs/Learn/JavaScript/First_steps/Arrays","doc":{"isMarkdown":true,"isTranslated":false,"isActive":true,"flaws":{},"title":"Arrays","mdn_url":"/en-US/docs/Learn/JavaScript/First_steps/Arrays","locale":"en-US","native":"English (US)","sidebarHTML":"<ol><li class=\"section\"><a href=\"/en-US/docs/Learn/Getting_started_with_the_web\">Complete beginners start here!</a></li><li><details><summary>Getting started with the web</summary><ol><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web\">Getting started with the web</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/Installing_basic_software\">Installing basic software</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/What_will_your_website_look_like\">What will your website look like?</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/Dealing_with_files\">Dealing with files</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/HTML_basics\">HTML basics</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/CSS_basics\">CSS basics</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/JavaScript_basics\">JavaScript basics</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/Publishing_your_website\">Publishing your website</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/How_the_Web_works\">How the web works</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/HTML\">HTML — Structuring the web</a></li><li><details><summary>Introduction to HTML</summary><ol><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML\">Introduction to HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Getting_started\">Getting started with HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/The_head_metadata_in_HTML\">What's in the head? Metadata in HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/HTML_text_fundamentals\">HTML text fundamentals</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Creating_hyperlinks\">Creating hyperlinks</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Advanced_text_formatting\">Advanced text formatting</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Document_and_website_structure\">Document and website structure</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML\">Debugging HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Marking_up_a_letter\">Marking up a letter</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Structuring_a_page_of_content\">Structuring a page of content</a></li></ol></details></li><li><details><summary>Multimedia and embedding</summary><ol><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding\">Multimedia and embedding</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Images_in_HTML\">Images in HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Video_and_audio_content\">Video and audio content</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Other_embedding_technologies\">From object to iframe — other embedding technologies</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Adding_vector_graphics_to_the_Web\">Adding vector graphics to the web</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Responsive_images\">Responsive images</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Mozilla_splash_page\">Mozilla splash page</a></li></ol></details></li><li><details><summary>HTML tables</summary><ol><li><a href=\"/en-US/docs/Learn/HTML/Tables\">HTML tables</a></li><li><a href=\"/en-US/docs/Learn/HTML/Tables/Basics\">HTML table basics</a></li><li><a href=\"/en-US/docs/Learn/HTML/Tables/Advanced\">HTML table advanced features and accessibility</a></li><li><a href=\"/en-US/docs/Learn/HTML/Tables/Structuring_planet_data\">Structuring planet data</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/CSS\">CSS — Styling the web</a></li><li><details><summary>CSS first steps</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/First_steps\">CSS first steps</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/What_is_CSS\">What is CSS?</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/Getting_started\">Getting started with CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/How_CSS_is_structured\">How CSS is structured</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/How_CSS_works\">How CSS works</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/Styling_a_biography_page\">Styling a biography page</a></li></ol></details></li><li><details><summary>CSS building blocks</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks\">CSS building blocks</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors\">CSS selectors</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Type_Class_and_ID_Selectors\">Type, class, and ID selectors</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Attribute_selectors\">Attribute selectors</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Pseudo-classes_and_pseudo-elements\">Pseudo-classes and pseudo-elements</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Combinators\">Combinators</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Cascade_and_inheritance\">Cascade, specificity, and inheritance</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Cascade_layers\">Cascade layers</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/The_box_model\">The box model</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Backgrounds_and_borders\">Backgrounds and borders</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Handling_different_text_directions\">Handling different text directions</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Overflowing_content\">Overflowing content</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Values_and_units\">CSS values and units</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Sizing_items_in_CSS\">Sizing items in CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Images_media_form_elements\">Images, media, and form elements</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Styling_tables\">Styling tables</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Advanced_styling_effects\">Advanced styling effects</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Debugging_CSS\">Debugging CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Organizing\">Organizing your CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Fundamental_CSS_comprehension\">Fundamental CSS comprehension</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Creating_fancy_letterheaded_paper\">Creating fancy letterheaded paper</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/A_cool_looking_box\">A cool-looking box</a></li></ol></details></li><li><details><summary>Styling text</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/Styling_text\">CSS styling text</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Fundamentals\">Fundamental text and font styling</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Styling_lists\">Styling lists</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Styling_links\">Styling links</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Web_fonts\">Web fonts</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Typesetting_a_homepage\">Typesetting a community school homepage</a></li></ol></details></li><li><details><summary>CSS layout</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout\">CSS layout</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Introduction\">Introduction to CSS layout</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Normal_Flow\">Normal Flow</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Flexbox\">Flexbox</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Grids\">Grids</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Floats\">Floats</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Positioning\">Positioning</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Multiple-column_Layout\">Multiple-column layout</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Responsive_Design\">Responsive design</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Media_queries\">Beginner's guide to media queries</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Legacy_Layout_Methods\">Legacy layout methods</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Supporting_Older_Browsers\">Supporting older browsers</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Fundamental_Layout_Comprehension\">Fundamental layout comprehension</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/JavaScript\">JavaScript — Dynamic client-side scripting</a></li><li><details open=\"\"><summary>JavaScript first steps</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps\">JavaScript first steps</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/What_is_JavaScript\">What is JavaScript?</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/A_first_splash\">A first splash into JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/What_went_wrong\">What went wrong? Troubleshooting JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Variables\">Storing the information you need — Variables</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Math\">Basic math in JavaScript — numbers and operators</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Strings\">Handling text — strings in JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods\">Useful string methods</a></li><li><em><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Arrays\" aria-current=\"page\">Arrays</a></em></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Silly_story_generator\">Silly story generator</a></li></ol></details></li><li><details><summary>JavaScript building blocks</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks\">JavaScript building blocks</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/conditionals\">Making decisions in your code — conditionals</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Looping_code\">Looping code</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Functions\">Functions — reusable blocks of code</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Build_your_own_function\">Build your own function</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Return_values\">Function return values</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Events\">Introduction to events</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Event_bubbling\">Event bubbling</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Image_gallery\">Image gallery</a></li></ol></details></li><li><details><summary>Introducing JavaScript objects</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Objects\">Introducing JavaScript objects</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Basics\">JavaScript object basics</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Object_prototypes\">Object prototypes</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Object-oriented_programming\">Object-oriented programming</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Classes_in_JavaScript\">Classes in JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/JSON\">Working with JSON</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Object_building_practice\">Object building practice</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Adding_bouncing_balls_features\">Adding features to our bouncing balls demo</a></li></ol></details></li><li><details><summary>Asynchronous JavaScript</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous\">Asynchronous JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Introducing\">Introducing asynchronous JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Promises\">How to use promises</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Implementing_a_promise-based_API\">How to implement a promise-based API</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Introducing_workers\">Introducing workers</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Sequencing_animations\">Sequencing animations</a></li></ol></details></li><li><details><summary>Client-side web APIs</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs\">Client-side web APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Introduction\">Introduction to web APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Manipulating_documents\">Manipulating documents</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Fetching_data\">Fetching data from the server</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Third_party_APIs\">Third-party APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Drawing_graphics\">Drawing graphics</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Video_and_audio_APIs\">Video and Audio APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Client-side_storage\">Client-side storage</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Forms\">Web forms — Working with user data</a></li><li><details><summary>Web form building blocks</summary><ol><li><a href=\"/en-US/docs/Learn/Forms\">Web form building blocks</a></li><li><a href=\"/en-US/docs/Learn/Forms/Your_first_form\">Your first form</a></li><li><a href=\"/en-US/docs/Learn/Forms/How_to_structure_a_web_form\">How to structure a web form</a></li><li><a href=\"/en-US/docs/Learn/Forms/Basic_native_form_controls\">Basic native form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/HTML5_input_types\">The HTML5 input types</a></li><li><a href=\"/en-US/docs/Learn/Forms/Other_form_controls\">Other form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/Styling_web_forms\">Styling web forms</a></li><li><a href=\"/en-US/docs/Learn/Forms/Advanced_form_styling\">Advanced form styling</a></li><li><a href=\"/en-US/docs/Learn/Forms/UI_pseudo-classes\">UI pseudo-classes</a></li><li><a href=\"/en-US/docs/Learn/Forms/Form_validation\">Client-side form validation</a></li><li><a href=\"/en-US/docs/Learn/Forms/Sending_and_retrieving_form_data\">Sending form data</a></li></ol></details></li><li><details><summary>Advanced web form techniques</summary><ol><li><a href=\"/en-US/docs/Learn/Forms/How_to_build_custom_form_controls\">How to build custom form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/Sending_forms_through_JavaScript\">Sending forms through JavaScript</a></li><li><a href=\"/en-US/docs/Learn/Forms/Property_compatibility_table_for_form_controls\">CSS property compatibility table for form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/HTML_forms_in_legacy_browsers\">HTML forms in legacy browsers</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Accessibility\">Accessibility — Make the web usable by everyone</a></li><li><details><summary>Accessibility guides</summary><ol><li><a href=\"/en-US/docs/Learn/Accessibility\">Accessibility</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/What_is_accessibility\">What is accessibility?</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/HTML\">HTML: A good basis for accessibility</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/CSS_and_JavaScript\">CSS and JavaScript accessibility best practices</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/WAI-ARIA_basics\">WAI-ARIA basics</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/Multimedia\">Accessible multimedia</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/Mobile\">Mobile accessibility</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/Accessibility_troubleshooting\">Assessment: Accessibility troubleshooting</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Performance\">Performance — Making websites fast and responsive</a></li><li><details><summary>Performance guides</summary><ol><li><a href=\"/en-US/docs/Learn/Performance\">Web performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/why_web_performance\">The \"why\" of web performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/What_is_web_performance\">What is web performance?</a></li><li><a href=\"/en-US/docs/Learn/Performance/Perceived_performance\">Perceived performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/Measuring_performance\">Measuring performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/Multimedia\">Multimedia: Images</a></li><li><a href=\"/en-US/docs/Learn/Performance/video\">Multimedia: video</a></li><li><a href=\"/en-US/docs/Learn/Performance/JavaScript\">JavaScript performance optimization</a></li><li><a href=\"/en-US/docs/Learn/Performance/HTML\">HTML performance optimization</a></li><li><a href=\"/en-US/docs/Learn/Performance/CSS\">CSS performance optimization</a></li><li><a href=\"/en-US/docs/Learn/Performance/business_case_for_performance\">The business case for web performance</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/MathML\">MathML — Writing mathematics with MathML</a></li><li><details><summary>MathML first steps</summary><ol><li><a href=\"/en-US/docs/Learn/MathML/First_steps\">MathML first steps</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Getting_started\">Getting started with MathML</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Text_containers\">MathML Text Containers</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Fractions_and_roots\">MathML fractions and roots</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Scripts\">MathML scripted elements</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Tables\">MathML tables</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Three_famous_mathematical_formulas\">Three famous mathematical formulas</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/../Games\">Games — Developing games for the web</a></li><li><details><summary>Guides and tutorials</summary><ol><li><a href=\"/en-US/docs/Games/Introduction\">Introduction to game development for the Web</a></li><li><a href=\"/en-US/docs/Games/Techniques\">Techniques for game development</a></li><li><a href=\"/en-US/docs/Games/Tutorials\">Tutorials</a></li><li><a href=\"/en-US/docs/Games/Publishing_games\">Publishing games</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Tools_and_testing\">Tools and testing</a></li><li><details><summary>Client-side web development tools</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools\">Understanding client-side web development tools</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Overview\">Client-side tooling overview</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Command_line\">Command line crash course</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Package_management\">Package management basics</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Introducing_complete_toolchain\">Introducing a complete toolchain</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Deployment\">Deploying our app</a></li></ol></details></li><li><details><summary>Introduction to client-side frameworks</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Introduction\">Introduction to client-side frameworks</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Main_features\">Framework main features</a></li></ol></details></li><li><details><summary>React</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_getting_started\">Getting started with React</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_todo_list_beginning\">Beginning our React todo list</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_components\">Componentizing our React app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_events_state\">React interactivity: Events and state</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_filtering_conditional_rendering\">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_accessibility\">Accessibility in React</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_resources\">React resources</a></li></ol></details></li><li><details><summary>Ember</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_getting_started\">Getting started with Ember</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_structure_componentization\">Ember app structure and componentization</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_interactivity_events_state\">Ember interactivity: Events, classes and state</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_conditional_footer\">Ember Interactivity: Footer functionality, conditional rendering</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_routing\">Routing in Ember</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_resources\">Ember resources and troubleshooting</a></li></ol></details></li><li><details><summary>Vue</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_getting_started\">Getting started with Vue</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_first_component\">Creating our first Vue component</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_rendering_lists\">Rendering a list of Vue components</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_methods_events_models\">Adding a new todo form: Vue events, methods, and models</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_styling\">Styling Vue components with CSS</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_computed_properties\">Using Vue computed properties</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_conditional_rendering\">Vue conditional rendering: editing existing todos</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_refs_focus_management\">Vue refs and lifecycle methods for focus management</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_resources\">Vue resources</a></li></ol></details></li><li><details><summary>Svelte</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_getting_started\">Getting started with Svelte</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_Todo_list_beginning\">Starting our Svelte to-do list app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_variables_props\">Dynamic behavior in Svelte: working with variables and props</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_components\">Componentizing our Svelte app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_reactivity_lifecycle_accessibility\">Advanced Svelte: Reactivity, lifecycle, accessibility</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_stores\">Working with Svelte stores</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_TypeScript\">TypeScript support in Svelte</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_deployment_next\">Deployment and next steps</a></li></ol></details></li><li><details><summary>Angular</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_getting_started\">Getting started with Angular</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_todo_list_beginning\">Beginning our Angular todo list app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_styling\">Styling our Angular app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_item_component\">Creating an item component</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_filtering\">Filtering our to-do items</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_building\">Building Angular applications and further resources</a></li></ol></details></li><li><details><summary>Git and GitHub</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/GitHub\">Git and GitHub</a></li></ol></details></li><li><details><summary>Cross browser testing</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing\">Cross browser testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Introduction\">Introduction to cross-browser testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Testing_strategies\">Strategies for carrying out testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/HTML_and_CSS\">Handling common HTML and CSS problems</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/JavaScript\">Handling common JavaScript problems</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Accessibility\">Handling common accessibility problems</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Feature_detection\">Implementing feature detection</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Automated_testing\">Introduction to automated testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Your_own_automation_environment\">Setting up your own test automation environment</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Server-side\">Server-side website programming</a></li><li><details><summary>First steps</summary><ol><li><a href=\"/en-US/docs/Learn/Server-side/First_steps\">Server-side website programming first steps</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Introduction\">Introduction to the server side</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Client-Server_overview\">Client-Server Overview</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Web_frameworks\">Server-side web frameworks</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Website_security\">Website security</a></li></ol></details></li><li><details><summary>Django web framework (Python)</summary><ol><li><a href=\"/en-US/docs/Learn/Server-side/Django\">Django Web Framework (Python)</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Introduction\">Django introduction</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/development_environment\">Setting up a Django development environment</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Tutorial_local_library_website\">Django Tutorial: The Local Library website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/skeleton_website\">Django Tutorial Part 2: Creating a skeleton website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Models\">Django Tutorial Part 3: Using models</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Admin_site\">Django Tutorial Part 4: Django admin site</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Home_page\">Django Tutorial Part 5: Creating our home page</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Generic_views\">Django Tutorial Part 6: Generic list and detail views</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Sessions\">Django Tutorial Part 7: Sessions framework</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Authentication\">Django Tutorial Part 8: User authentication and permissions</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Forms\">Django Tutorial Part 9: Working with forms</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Testing\">Django Tutorial Part 10: Testing a Django web application</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Deployment\">Django Tutorial Part 11: Deploying Django to production</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/web_application_security\">Django web application security</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/django_assessment_blog\">Assessment: DIY Django mini blog</a></li></ol></details></li><li><details><summary>Express Web Framework (Node.js/JavaScript)</summary><ol><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs\">Express web framework (Node.js/JavaScript)</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/Introduction\">Express/Node introduction</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/development_environment\">Setting up a Node development environment</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/Tutorial_local_library_website\">Express Tutorial: The Local Library website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/skeleton_website\">Express Tutorial Part 2: Creating a skeleton website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/mongoose\">Express Tutorial Part 3: Using a Database (with Mongoose)</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/routes\">Express Tutorial Part 4: Routes and controllers</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/Displaying_data\">Express Tutorial Part 5: Displaying library data</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/forms\">Express Tutorial Part 6: Working with forms</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/deployment\">Express Tutorial Part 7: Deploying to production</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Common_questions\">Further resources</a></li><li><details><summary>Common questions</summary><ol><li><a href=\"/en-US/docs/Learn/Common_questions\">Common questions</a></li><li><a href=\"/en-US/docs/Learn/HTML/Howto\">Use HTML to solve common problems</a></li><li><a href=\"/en-US/docs/Learn/CSS/Howto\">Use CSS to solve common problems</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Howto\">Solve common problems in your JavaScript code</a></li><li><a href=\"/en-US/docs/Learn/Common_questions/Web_mechanics\">Web mechanics</a></li><li><a href=\"/en-US/docs/Learn/Common_questions/Tools_and_setup\">Tools and setup</a></li><li><a href=\"/en-US/docs/Learn/Common_questions/Design_and_accessibility\">Design and accessibility</a></li></ol></details></li></ol>","sidebarMacro":"LearnSidebar","body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<ul class=\"prev-next\">\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods\"><span class=\"button-wrap\"> Previous </span></a></li>\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/JavaScript/First_steps\"><span class=\"button-wrap\"> Overview: JavaScript first steps</span></a></li>\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/JavaScript/First_steps/Silly_story_generator\"><span class=\"button-wrap\"> Next </span></a></li>\n</ul>\n<p>In the final article of this module, we'll look at arrays — a neat way of storing a list of data items under a single variable name. Here we look at why this is useful, then explore how to create an array, retrieve, add, and remove items stored in an array, and more besides.</p>\n<figure class=\"table-container\"><table>\n <tbody>\n <tr>\n <th scope=\"row\">Prerequisites:</th>\n <td>\n A basic understanding of HTML and CSS, an\n understanding of what JavaScript is.\n </td>\n </tr>\n <tr>\n <th scope=\"row\">Objective:</th>\n <td>To understand what arrays are and how to manipulate them in JavaScript.</td>\n </tr>\n </tbody>\n</table></figure>"}},{"type":"prose","value":{"id":"what_is_an_array","title":"What is an array?","isH3":false,"content":"<p>Arrays are generally described as \"list-like objects\"; they are basically single objects that contain multiple values stored in a list. Array objects can be stored in variables and dealt with in much the same way as any other type of value, the difference being that we can access each value inside the list individually, and do super useful and efficient things with the list, like loop through it and do the same thing to every value. Maybe we've got a series of product items and their prices stored in an array, and we want to loop through them all and print them out on an invoice, while totaling all the prices together and printing out the total price at the bottom.</p>\n<p>If we didn't have arrays, we'd have to store every item in a separate variable, then call the code that does the printing and adding separately for each item. This would be much longer to write out, less efficient, and more error-prone. If we had 10 items to add to the invoice it would already be annoying, but what about 100 items, or 1000? We'll return to this example later on in the article.</p>\n<p>As in previous articles, let's learn about the real basics of arrays by entering some examples into <a href=\"/en-US/docs/Learn/Common_questions/Tools_and_setup/What_are_browser_developer_tools\">browser developer console</a>.</p>"}},{"type":"prose","value":{"id":"creating_arrays","title":"Creating arrays","isH3":false,"content":"<p>Arrays consist of square brackets and items that are separated by commas.</p>\n<ol>\n <li>\n <p>Suppose we want to store a shopping list in an array. Paste the following code into the console:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const shopping = [\"bread\", \"milk\", \"cheese\", \"hummus\", \"noodles\"];\nconsole.log(shopping);\n</code></pre></div>\n </li>\n <li>\n <p>In the above example, each item is a string, but in an array we can store various data types — strings, numbers, objects, and even other arrays. We can also mix data types in a single array — we do not have to limit ourselves to storing only numbers in one array, and in another only strings. For example:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const sequence = [1, 1, 2, 3, 5, 8, 13];\nconst random = [\"tree\", 795, [0, 1, 2]];\n</code></pre></div>\n </li>\n <li>\n <p>Before proceeding, create a few example arrays.</p>\n </li>\n</ol>"}},{"type":"prose","value":{"id":"finding_the_length_of_an_array","title":"Finding the length of an array","isH3":false,"content":"<p>You can find out the length of an array (how many items are in it) in exactly the same way as you find out the length (in characters) of a string — by using the <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/length\"><code>length</code></a> property. Try the following:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const shopping = [\"bread\", \"milk\", \"cheese\", \"hummus\", \"noodles\"];\nconsole.log(shopping.length); // 5\n</code></pre></div>"}},{"type":"prose","value":{"id":"accessing_and_modifying_array_items","title":"Accessing and modifying array items","isH3":false,"content":"<p>Items in an array are numbered, starting from zero. This number is called the item's <em>index</em>. So the first item has index 0, the second has index 1, and so on. You can access individual items in the array using bracket notation and supplying the item's index, in the same way that you <a href=\"/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods#retrieving_a_specific_string_character\">accessed the letters in a string</a>.</p>\n<ol>\n <li>\n <p>Enter the following into your console:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const shopping = [\"bread\", \"milk\", \"cheese\", \"hummus\", \"noodles\"];\nconsole.log(shopping[0]);\n// returns \"bread\"\n</code></pre></div>\n </li>\n <li>\n <p>You can also modify an item in an array by giving a single array item a new value. Try this:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const shopping = [\"bread\", \"milk\", \"cheese\", \"hummus\", \"noodles\"];\nshopping[0] = \"tahini\";\nconsole.log(shopping);\n// shopping will now return [ \"tahini\", \"milk\", \"cheese\", \"hummus\", \"noodles\" ]\n</code></pre></div>\n <div class=\"notecard note\">\n <p><strong>Note:</strong> We've said it before, but just as a reminder — JavaScript starts indexing arrays at zero!</p>\n </div>\n </li>\n <li>\n <p>Note that an array inside an array is called a multidimensional array. You can access an item inside an array that is itself inside another array by chaining two sets of square brackets together. For example, to access one of the items inside the array that is the third item inside the <code>random</code> array (see previous section), we could do something like this:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const random = [\"tree\", 795, [0, 1, 2]];\nrandom[2][2];\n</code></pre></div>\n </li>\n <li>\n <p>Try making some more modifications to your array examples before moving on. Play around a bit, and see what works and what doesn't.</p>\n </li>\n</ol>"}},{"type":"prose","value":{"id":"finding_the_index_of_items_in_an_array","title":"Finding the index of items in an array","isH3":false,"content":"<p>\n If you don't know the index of an item, you can use the <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf\"><code>indexOf()</code></a> method.\n The <code>indexOf()</code> method takes an item as an argument and will either return the item's index or <code>-1</code> if the item is not in the array:\n</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const birds = [\"Parrot\", \"Falcon\", \"Owl\"];\nconsole.log(birds.indexOf(\"Owl\")); // 2\nconsole.log(birds.indexOf(\"Rabbit\")); // -1\n</code></pre></div>"}},{"type":"prose","value":{"id":"adding_items","title":"Adding items","isH3":false,"content":"<p>To add one or more items to the end of an array we can use <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push\"><code>push()</code></a>. Note that you need to include one or more items that you want to add to the end of your array.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const cities = [\"Manchester\", \"Liverpool\"];\ncities.push(\"Cardiff\");\nconsole.log(cities); // [ \"Manchester\", \"Liverpool\", \"Cardiff\" ]\ncities.push(\"Bradford\", \"Brighton\");\nconsole.log(cities); // [ \"Manchester\", \"Liverpool\", \"Cardiff\", \"Bradford\", \"Brighton\" ]\n</code></pre></div>\n<p>The new length of the array is returned when the method call completes. If you wanted to store the new array length in a variable, you could do something like this:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const cities = [\"Manchester\", \"Liverpool\"];\nconst newLength = cities.push(\"Bristol\");\nconsole.log(cities); // [ \"Manchester\", \"Liverpool\", \"Bristol\" ]\nconsole.log(newLength); // 3\n</code></pre></div>\n<p>To add an item to the start of the array, use <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/unshift\"><code>unshift()</code></a>:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const cities = [\"Manchester\", \"Liverpool\"];\ncities.unshift(\"Edinburgh\");\nconsole.log(cities); // [ \"Edinburgh\", \"Manchester\", \"Liverpool\" ]\n</code></pre></div>"}},{"type":"prose","value":{"id":"removing_items","title":"Removing items","isH3":false,"content":"<p>To remove the last item from the array, use <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/pop\"><code>pop()</code></a>.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const cities = [\"Manchester\", \"Liverpool\"];\ncities.pop();\nconsole.log(cities); // [ \"Manchester\" ]\n</code></pre></div>\n<p>The <code>pop()</code> method returns the item that was removed. To save that item in a new variable, you could do this:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const cities = [\"Manchester\", \"Liverpool\"];\nconst removedCity = cities.pop();\nconsole.log(removedCity); // \"Liverpool\"\n</code></pre></div>\n<p>To remove the first item from an array, use <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/shift\"><code>shift()</code></a>:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const cities = [\"Manchester\", \"Liverpool\"];\ncities.shift();\nconsole.log(cities); // [ \"Liverpool\" ]\n</code></pre></div>\n<p>If you know the index of an item, you can remove it from the array using <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice\"><code>splice()</code></a>:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const cities = [\"Manchester\", \"Liverpool\", \"Edinburgh\", \"Carlisle\"];\nconst index = cities.indexOf(\"Liverpool\");\nif (index !== -1) {\n cities.splice(index, 1);\n}\nconsole.log(cities); // [ \"Manchester\", \"Edinburgh\", \"Carlisle\" ]\n</code></pre></div>\n<p>In this call to <code>splice()</code>, the first argument says where to start removing items, and the second argument says how many items should be removed. So you can remove more than one item:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const cities = [\"Manchester\", \"Liverpool\", \"Edinburgh\", \"Carlisle\"];\nconst index = cities.indexOf(\"Liverpool\");\nif (index !== -1) {\n cities.splice(index, 2);\n}\nconsole.log(cities); // [ \"Manchester\", \"Carlisle\" ]\n</code></pre></div>"}},{"type":"prose","value":{"id":"accessing_every_item","title":"Accessing every item","isH3":false,"content":"<p>Very often you will want to access every item in the array. You can do this using the <a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/for...of\"><code>for...of</code></a> statement:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const birds = [\"Parrot\", \"Falcon\", \"Owl\"];\n\nfor (const bird of birds) {\n console.log(bird);\n}\n</code></pre></div>\n<p>Sometimes you will want to do the same thing to each item in an array, leaving you with an array containing the changed items. You can do this using <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map\"><code>map()</code></a>. The code below takes an array of numbers and doubles each number:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function double(number) {\n return number * 2;\n}\nconst numbers = [5, 2, 7, 6];\nconst doubled = numbers.map(double);\nconsole.log(doubled); // [ 10, 4, 14, 12 ]\n</code></pre></div>\n<p>We give a function to the <code>map()</code>, and <code>map()</code> calls the function once for each item in the array, passing in the item. It then adds the return value from each function call to a new array, and finally returns the new array.</p>\n<p>Sometimes you'll want to create a new array containing only the items in the original array that match some test. You can do that using <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter\"><code>filter()</code></a>. The code below takes an array of strings and returns an array containing just the strings that are greater than 8 characters long:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function isLong(city) {\n return city.length > 8;\n}\nconst cities = [\"London\", \"Liverpool\", \"Totnes\", \"Edinburgh\"];\nconst longer = cities.filter(isLong);\nconsole.log(longer); // [ \"Liverpool\", \"Edinburgh\" ]\n</code></pre></div>\n<p>Like <code>map()</code>, we give a function to the <code>filter()</code> method, and <code>filter()</code> calls this function for every item in the array, passing in the item. If the function returns <code>true</code>, then the item is added to a new array. Finally it returns the new array.</p>"}},{"type":"prose","value":{"id":"converting_between_strings_and_arrays","title":"Converting between strings and arrays","isH3":false,"content":"<p>Often you'll be presented with some raw data contained in a big long string, and you might want to separate the useful items out into a more useful form and then do things to them, like display them in a data table. To do this, we can use the <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split\"><code>split()</code></a> method. In its simplest form, this takes a single parameter, the character you want to separate the string at, and returns the substrings between the separator as items in an array.</p>\n<div class=\"notecard note\">\n <p><strong>Note:</strong> Okay, this is technically a string method, not an array method, but we've put it in with arrays as it goes well here.</p>\n</div>\n<ol>\n <li>\n <p>Let's play with this, to see how it works. First, create a string in your console:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const data = \"Manchester,London,Liverpool,Birmingham,Leeds,Carlisle\";\n</code></pre></div>\n </li>\n <li>\n <p>Now let's split it at each comma:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const cities = data.split(\",\");\ncities;\n</code></pre></div>\n </li>\n <li>\n <p>Finally, try finding the length of your new array, and retrieving some items from it:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>cities.length;\ncities[0]; // the first item in the array\ncities[1]; // the second item in the array\ncities[cities.length - 1]; // the last item in the array\n</code></pre></div>\n </li>\n <li>\n <p>You can also go the opposite way using the <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join\"><code>join()</code></a> method. Try the following:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const commaSeparated = cities.join(\",\");\ncommaSeparated;\n</code></pre></div>\n </li>\n <li>\n <p>Another way of converting an array to a string is to use the <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toString\"><code>toString()</code></a> method. <code>toString()</code> is arguably simpler than <code>join()</code> as it doesn't take a parameter, but more limiting. With <code>join()</code> you can specify different separators, whereas <code>toString()</code> always uses a comma. (Try running Step 4 with a different character than a comma.)</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const dogNames = [\"Rocket\", \"Flash\", \"Bella\", \"Slugger\"];\ndogNames.toString(); // Rocket,Flash,Bella,Slugger\n</code></pre></div>\n </li>\n</ol>"}},{"type":"prose","value":{"id":"active_learning_printing_those_products","title":"Active learning: Printing those products","isH3":false,"content":"<p>Let's return to the example we described earlier — printing out product names and prices on an invoice, then totaling the prices and printing them at the bottom. In the editable example below there are comments containing numbers — each of these marks a place where you have to add something to the code. They are as follows:</p>\n<ol>\n <li>Below the <code>// number 1</code> comment are a number of strings, each one containing a product name and price separated by a colon. We'd like you to turn this into an array and store it in an array called <code>products</code>.</li>\n <li>Below the <code>// number 2</code> comment, start a <code>for...of()</code> loop to go through every item in the <code>products</code> array.</li>\n <li>Below the <code>// number 3</code> comment we want you to write a line of code that splits the current array item (<code>name:price</code>) into two separate items, one containing just the name and one containing just the price. If you are not sure how to do this, consult the <a href=\"/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods\">Useful string methods</a> article for some help, or even better, look at the <a href=\"#converting_between_strings_and_arrays\">Converting between strings and arrays</a> section of this article.</li>\n <li>As part of the above line of code, you'll also want to convert the price from a string to a number. If you can't remember how to do this, check out the <a href=\"/en-US/docs/Learn/JavaScript/First_steps/Strings#numbers_vs._strings\">first strings article</a>.</li>\n <li>There is a variable called <code>total</code> that is created and given a value of 0 at the top of the code. Inside the loop (below <code>// number 4</code>) we want you to add a line that adds the current item price to that total in each iteration of the loop, so that at the end of the code the correct total is printed onto the invoice. You might need an <a href=\"/en-US/docs/Learn/JavaScript/First_steps/Math#assignment_operators\">assignment operator</a> to do this.</li>\n <li>We want you to change the line just below <code>// number 5</code> so that the <code>itemText</code> variable is made equal to \"current item name — $current item price\", for example \"Shoes — $23.99\" in each case, so the correct information for each item is printed on the invoice. This is just simple string concatenation, which should be familiar to you.</li>\n <li>Finally, below the <code>// number 6</code> comment, you'll need to add a <code>}</code> to mark the end of the <code>for...of()</code> loop.</li>\n</ol>\n<div class=\"code-example\"><pre class=\"brush: html hidden notranslate\"><code><h2>Live output</h2>\n\n<div class=\"output\" style=\"min-height: 150px;\">\n <ul></ul>\n\n <p></p>\n</div>\n\n<h2>Editable code</h2>\n\n<p class=\"a11y-label\">\n Press Esc to move focus away from the code area (Tab inserts a tab character).\n</p>\n\n<textarea id=\"code\" class=\"playable-code\" style=\"height: 410px;width: 95%\">\nconst list = document.querySelector('.output ul');\nconst totalBox = document.querySelector('.output p');\nlet total = 0;\nlist.textContent = \"\";\ntotalBox.textContent = \"\";\n// number 1\n 'Underpants:6.99'\n 'Socks:5.99'\n 'T-shirt:14.99'\n 'Trousers:31.99'\n 'Shoes:23.99';\n\n// number 2\n\n // number 3\n\n // number 4\n\n // number 5\n let itemText = 0;\n\n const listItem = document.createElement('li');\n listItem.textContent = itemText;\n list.appendChild(listItem);\n\n// number 6\n\ntotalBox.textContent = 'Total: $' + total.toFixed(2);\n</textarea>\n\n<div class=\"playable-buttons\">\n <input id=\"reset\" type=\"button\" value=\"Reset\" />\n <input id=\"solution\" type=\"button\" value=\"Show solution\" />\n</div>\n</code></pre></div>\n<div class=\"code-example\"><pre class=\"brush: js hidden notranslate\"><code>const textarea = document.getElementById(\"code\");\nconst reset = document.getElementById(\"reset\");\nconst solution = document.getElementById(\"solution\");\nlet code = textarea.value;\nlet userEntry = textarea.value;\n\nfunction updateCode() {\n eval(textarea.value);\n}\n\nreset.addEventListener(\"click\", () => {\n textarea.value = code;\n userEntry = textarea.value;\n solutionEntry = jsSolution;\n solution.value = \"Show solution\";\n updateCode();\n});\n\nsolution.addEventListener(\"click\", () => {\n if (solution.value === \"Show solution\") {\n textarea.value = solutionEntry;\n solution.value = \"Hide solution\";\n } else {\n textarea.value = userEntry;\n solution.value = \"Show solution\";\n }\n updateCode();\n});\n\nconst jsSolution = `const list = document.querySelector('.output ul');\nconst totalBox = document.querySelector('.output p');\nlet total = 0;\nlist.textContent = \"\";\ntotalBox.textContent = \"\";\n\nconst products = [\n 'Underpants:6.99',\n 'Socks:5.99',\n 'T-shirt:14.99',\n 'Trousers:31.99',\n 'Shoes:23.99',\n];\n\nfor (const product of products) {\n const subArray = product.split(':');\n const name = subArray[0];\n const price = Number(subArray[1]);\n total += price;\n const itemText = \\`\\${name} — $\\${price}\\`;\n\n const listItem = document.createElement('li');\n listItem.textContent = itemText;\n list.appendChild(listItem);\n}\n\ntotalBox.textContent = \\`Total: $\\${total.toFixed(2)}\\`;`;\nlet solutionEntry = jsSolution;\n\ntextarea.addEventListener(\"input\", updateCode);\nwindow.addEventListener(\"load\", updateCode);\n\n// stop tab key tabbing out of textarea and\n// make it write a tab at the caret position instead\n\ntextarea.onkeydown = (event) => {\n if (event.code === \"Tab\") {\n event.preventDefault();\n insertAtCaret(\"\\t\");\n }\n if (event.code === \"Escape\") {\n textarea.blur();\n }\n};\n\nfunction insertAtCaret(text) {\n const scrollPos = textarea.scrollTop;\n let caretPos = textarea.selectionStart;\n const front = textarea.value.substring(0, caretPos);\n const back = textarea.value.substring(\n textarea.selectionEnd,\n textarea.value.length,\n );\n\n textarea.value = front + text + back;\n caretPos += text.length;\n textarea.selectionStart = caretPos;\n textarea.selectionEnd = caretPos;\n textarea.focus();\n textarea.scrollTop = scrollPos;\n}\n\n// Update the saved userCode every time the user updates the text area code\n\ntextarea.onkeyup = () => {\n // We only want to save the state when the user code is being shown,\n // not the solution, so that solution is not saved over the user code\n if (solution.value === \"Show solution\") {\n userEntry = textarea.value;\n } else {\n solutionEntry = textarea.value;\n }\n updateCode();\n};\n</code></pre></div>\n<div class=\"code-example\"><pre class=\"brush: css hidden notranslate\"><code>html {\n font-family: sans-serif;\n}\n\nh2 {\n font-size: 16px;\n}\n\n.a11y-label {\n margin: 0;\n text-align: right;\n font-size: 0.7rem;\n width: 98%;\n}\n\nbody {\n margin: 10px;\n background-color: #f5f9fa;\n}\n</code></pre></div><div class=\"code-example\"><div class=\"example-header\"></div><iframe class=\"sample-code-frame\" title=\"Active learning Printing those products sample\" id=\"frame_active_learning_printing_those_products\" width=\"100%\" height=\"750\" src=\"about:blank\" data-live-path=\"/en-US/docs/Learn/JavaScript/First_steps/Arrays\" data-live-id=\"active_learning_printing_those_products\" sandbox=\"allow-same-origin allow-scripts\" loading=\"lazy\"></iframe></div>"}},{"type":"prose","value":{"id":"active_learning_top_5_searches","title":"Active learning: Top 5 searches","isH3":false,"content":"<p>A good use for array methods like <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push\"><code>push()</code></a> and <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/pop\"><code>pop()</code></a> is when you are maintaining a record of currently active items in a web app. In an animated scene for example, you might have an array of objects representing the background graphics currently displayed, and you might only want 50 displayed at once, for performance or clutter reasons. As new objects are created and added to the array, older ones can be deleted from the array to maintain the desired number.</p>\n<p>In this example we're going to show a much simpler use — here we're giving you a fake search site, with a search box. The idea is that when terms are entered in the search box, the top 5 previous search terms are displayed in the list. When the number of terms goes over 5, the last term starts being deleted each time a new term is added to the top, so the 5 previous terms are always displayed.</p>\n<div class=\"notecard note\">\n <p><strong>Note:</strong> In a real search app, you'd probably be able to click the previous search terms to return to previous searches, and it would display actual search results! We are just keeping it simple for now.</p>\n</div>\n<p>To complete the app, we need you to:</p>\n<ol>\n <li>Add a line below the <code>// number 1</code> comment that adds the current value entered into the search input to the start of the array. This can be retrieved using <code>searchInput.value</code>.</li>\n <li>Add a line below the <code>// number 2</code> comment that removes the value currently at the end of the array.</li>\n</ol>\n<div class=\"code-example\"><pre class=\"brush: html hidden notranslate\"><code><h2>Live output</h2>\n<div class=\"output\" style=\"min-height: 150px;\">\n <input type=\"text\" /><button>Search</button>\n\n <ul></ul>\n</div>\n\n<h2>Editable code</h2>\n\n<p class=\"a11y-label\">\n Press Esc to move focus away from the code area (Tab inserts a tab character).\n</p>\n\n<textarea id=\"code\" class=\"playable-code\" style=\"height: 370px; width: 95%\">\nconst list = document.querySelector('.output ul');\nconst searchInput = document.querySelector('.output input');\nconst searchBtn = document.querySelector('.output button');\n\nlist.textContent = \"\";\n\nconst myHistory = [];\nconst MAX_HISTORY = 5;\n\nsearchBtn.onclick = () => {\n // we will only allow a term to be entered if the search input isn't empty\n if (searchInput.value !== '') {\n // number 1\n\n // empty the list so that we don't display duplicate entries\n // the display is regenerated every time a search term is entered.\n list.textContent = \"\";\n\n // loop through the array, and display all the search terms in the list\n for (const itemText of myHistory) {\n const listItem = document.createElement('li');\n listItem.textContent = itemText;\n list.appendChild(listItem);\n }\n\n // If the array length is 5 or more, remove the oldest search term\n if (myHistory.length >= MAX_HISTORY) {\n // number 2\n }\n\n // empty the search input and focus it, ready for the next term to be entered\n searchInput.value = '';\n searchInput.focus();\n }\n}\n</textarea>\n\n<div class=\"playable-buttons\">\n <input id=\"reset\" type=\"button\" value=\"Reset\" />\n <input id=\"solution\" type=\"button\" value=\"Show solution\" />\n</div>\n</code></pre></div>\n<div class=\"code-example\"><pre class=\"brush: css hidden notranslate\"><code>html {\n font-family: sans-serif;\n}\n\nh2 {\n font-size: 16px;\n}\n\n.a11y-label {\n margin: 0;\n text-align: right;\n font-size: 0.7rem;\n width: 98%;\n}\n\nbody {\n margin: 10px;\n background: #f5f9fa;\n}\n</code></pre></div>\n<div class=\"code-example\"><pre class=\"brush: js hidden notranslate\"><code>const textarea = document.getElementById(\"code\");\nconst reset = document.getElementById(\"reset\");\nconst solution = document.getElementById(\"solution\");\nlet code = textarea.value;\nlet userEntry = textarea.value;\n\nfunction updateCode() {\n eval(textarea.value);\n}\n\nreset.addEventListener(\"click\", () => {\n textarea.value = code;\n userEntry = textarea.value;\n solutionEntry = jsSolution;\n solution.value = \"Show solution\";\n updateCode();\n});\n\nsolution.addEventListener(\"click\", () => {\n if (solution.value === \"Show solution\") {\n textarea.value = solutionEntry;\n solution.value = \"Hide solution\";\n } else {\n textarea.value = userEntry;\n solution.value = \"Show solution\";\n }\n updateCode();\n});\n\nconst jsSolution = `const list = document.querySelector('.output ul');\nconst searchInput = document.querySelector('.output input');\nconst searchBtn = document.querySelector('.output button');\n\nlist.textContent = \"\";\n\nconst myHistory = [];\nconst MAX_HISTORY = 5;\n\nsearchBtn.onclick = () => {\n // we will only allow a term to be entered if the search input isn't empty\n if (searchInput.value !== '') {\n myHistory.unshift(searchInput.value);\n\n // empty the list so that we don't display duplicate entries\n // the display is regenerated every time a search term is entered.\n list.textContent = \"\";\n\n // loop through the array, and display all the search terms in the list\n for (const itemText of myHistory) {\n const listItem = document.createElement('li');\n listItem.textContent = itemText;\n list.appendChild(listItem);\n }\n\n // If the array length is 5 or more, remove the oldest search term\n if (myHistory.length >= MAX_HISTORY) {\n myHistory.pop();\n }\n\n // empty the search input and focus it, ready for the next term to be entered\n searchInput.value = '';\n searchInput.focus();\n }\n}`;\nlet solutionEntry = jsSolution;\n\ntextarea.addEventListener(\"input\", updateCode);\nwindow.addEventListener(\"load\", updateCode);\n\n// stop tab key tabbing out of textarea and\n// make it write a tab at the caret position instead\n\ntextarea.onkeydown = (event) => {\n if (event.code === \"Tab\") {\n event.preventDefault();\n insertAtCaret(\"\\t\");\n }\n if (event.code === \"Escape\") {\n textarea.blur();\n }\n};\n\nfunction insertAtCaret(text) {\n const scrollPos = textarea.scrollTop;\n let caretPos = textarea.selectionStart;\n const front = textarea.value.substring(0, caretPos);\n const back = textarea.value.substring(\n textarea.selectionEnd,\n textarea.value.length,\n );\n\n textarea.value = front + text + back;\n caretPos += text.length;\n textarea.selectionStart = caretPos;\n textarea.selectionEnd = caretPos;\n textarea.focus();\n textarea.scrollTop = scrollPos;\n}\n\n// Update the saved userCode every time the user updates the text area code\n\ntextarea.onkeyup = () => {\n // We only want to save the state when the user code is being shown,\n // not the solution, so that solution is not saved over the user code\n if (solution.value === \"Show solution\") {\n userEntry = textarea.value;\n } else {\n solutionEntry = textarea.value;\n }\n updateCode();\n};\n</code></pre></div><div class=\"code-example\"><div class=\"example-header\"></div><iframe class=\"sample-code-frame\" title=\"Active learning Top 5 searches sample\" id=\"frame_active_learning_top_5_searches\" width=\"100%\" height=\"700\" src=\"about:blank\" data-live-path=\"/en-US/docs/Learn/JavaScript/First_steps/Arrays\" data-live-id=\"active_learning_top_5_searches\" sandbox=\"allow-same-origin allow-scripts\" loading=\"lazy\"></iframe></div>"}},{"type":"prose","value":{"id":"test_your_skills!","title":"Test your skills!","isH3":false,"content":"<p>You've reached the end of this article, but can you remember the most important information? You can find some further tests to verify that you've retained this information before you move on — see <a href=\"/en-US/docs/Learn/JavaScript/First_steps/Test_your_skills:_Arrays\">Test your skills: Arrays</a>.</p>"}},{"type":"prose","value":{"id":"conclusion","title":"Conclusion","isH3":false,"content":"<p>After reading through this article, we are sure you will agree that arrays seem pretty darn useful; you'll see them crop up everywhere in JavaScript, often in association with loops in order to do the same thing to every item in an array. We'll be teaching you all the useful basics there are to know about loops in the next module, but for now you should give yourself a clap and take a well-deserved break; you've worked through all the articles in this module!</p>\n<p>The only thing left to do is work through this module's assessment, which will test your understanding of the articles that came before it.</p>"}},{"type":"prose","value":{"id":"see_also","title":"See also","isH3":false,"content":"<ul>\n <li><a href=\"/en-US/docs/Web/JavaScript/Guide/Indexed_collections\">Indexed collections</a> — an advanced level guide to arrays and their cousins, typed arrays.</li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array\"><code>Array</code></a> — the <code>Array</code> object reference page — for a detailed reference guide to the features discussed in this page, and many more.</li>\n</ul><ul class=\"prev-next\">\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods\"><span class=\"button-wrap\"> Previous </span></a></li>\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/JavaScript/First_steps\"><span class=\"button-wrap\"> Overview: JavaScript first steps</span></a></li>\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/JavaScript/First_steps/Silly_story_generator\"><span class=\"button-wrap\"> Next </span></a></li>\n</ul>"}}],"toc":[{"text":"What is an array?","id":"what_is_an_array"},{"text":"Creating arrays","id":"creating_arrays"},{"text":"Finding the length of an array","id":"finding_the_length_of_an_array"},{"text":"Accessing and modifying array items","id":"accessing_and_modifying_array_items"},{"text":"Finding the index of items in an array","id":"finding_the_index_of_items_in_an_array"},{"text":"Adding items","id":"adding_items"},{"text":"Removing items","id":"removing_items"},{"text":"Accessing every item","id":"accessing_every_item"},{"text":"Converting between strings and arrays","id":"converting_between_strings_and_arrays"},{"text":"Active learning: Printing those products","id":"active_learning_printing_those_products"},{"text":"Active learning: Top 5 searches","id":"active_learning_top_5_searches"},{"text":"Test your skills!","id":"test_your_skills!"},{"text":"Conclusion","id":"conclusion"},{"text":"See also","id":"see_also"}],"summary":"In the final article of this module, we'll look at arrays — a neat way of storing a list of data items under a single variable name. Here we look at why this is useful, then explore how to create an array, retrieve, add, and remove items stored in an array, and more besides.","popularity":0.0176,"modified":"2024-07-26T02:12:21.000Z","other_translations":[{"locale":"de","title":"Arrays","native":"Deutsch"},{"locale":"es","title":"Arreglos","native":"Español"},{"locale":"fr","title":"Les tableaux","native":"Français"},{"locale":"ja","title":"配列","native":"日本語"},{"locale":"ko","title":"배열(Arrays)","native":"한국어"},{"locale":"pt-BR","title":"Arrays","native":"Português (do Brasil)"},{"locale":"ru","title":"Массивы","native":"Русский"},{"locale":"zh-CN","title":"数组","native":"中文 (简体)"},{"locale":"zh-TW","title":"Arrays","native":"正體中文 (繁體)"}],"pageType":"learn-module-chapter","source":{"folder":"en-us/learn/javascript/first_steps/arrays","github_url":"https://github.com/mdn/content/blob/main/files/en-us/learn/javascript/first_steps/arrays/index.md","last_commit_url":"https://github.com/mdn/content/commit/cde9330e9bbaddea72febf44dcc3a7db16fe1a11","filename":"index.md"},"short_title":"Arrays","parents":[{"uri":"/en-US/docs/Learn","title":"Guides"},{"uri":"/en-US/docs/Learn/JavaScript","title":"JavaScript — Dynamic client-side scripting"},{"uri":"/en-US/docs/Learn/JavaScript/First_steps","title":"JavaScript first steps"},{"uri":"/en-US/docs/Learn/JavaScript/First_steps/Arrays","title":"Arrays"}],"pageTitle":"Arrays - Learn web development | MDN","noIndexing":false}}</script></body></html>