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<!doctype html><html lang="en-US" prefix="og: https://ogp.me/ns#"><head><meta charSet="utf-8"/><meta name="viewport" content="width=device-width,initial-scale=1"/><link rel="icon" href="https://developer.mozilla.org/favicon-48x48.bc390275e955dacb2e65.png"/><link rel="apple-touch-icon" href="https://developer.mozilla.org/apple-touch-icon.528534bba673c38049c2.png"/><meta name="theme-color" content="#ffffff"/><link rel="manifest" href="https://developer.mozilla.org/manifest.f42880861b394dd4dc9b.json"/><link rel="search" type="application/opensearchdescription+xml" href="/opensearch.xml" title="MDN Web Docs"/><title>Making decisions in your code — conditionals - Learn web development | MDN</title><link rel="alternate" title="Entscheidungen in Ihrem Code treffen — Konditionalen" href="https://developer.mozilla.org/de/docs/Learn_web_development/Core/Scripting/Conditionals" hrefLang="de"/><link rel="alternate" title="Tomando decisiones en tu código — condicionales" href="https://developer.mozilla.org/es/docs/Learn_web_development/Core/Scripting/Conditionals" hrefLang="es"/><link rel="alternate" title="Prendre des décisions dans le code — conditions" href="https://developer.mozilla.org/fr/docs/Learn_web_development/Core/Scripting/Conditionals" hrefLang="fr"/><link rel="alternate" title="コードでの意思決定 — 条件文" href="https://developer.mozilla.org/ja/docs/Learn_web_development/Core/Scripting/Conditionals" hrefLang="ja"/><link rel="alternate" title="판단 내리기 — 조건문" href="https://developer.mozilla.org/ko/docs/Learn_web_development/Core/Scripting/Conditionals" hrefLang="ko"/><link rel="alternate" title="Tomando decisões no seu código — condicionais" href="https://developer.mozilla.org/pt-BR/docs/Learn_web_development/Core/Scripting/Conditionals" hrefLang="pt"/><link rel="alternate" title="Принятие решений в вашем коде — условные конструкции" href="https://developer.mozilla.org/ru/docs/Learn_web_development/Core/Scripting/Conditionals" hrefLang="ru"/><link rel="alternate" title="在代码中做决定——条件语句" href="https://developer.mozilla.org/zh-CN/docs/Learn_web_development/Core/Scripting/Conditionals" hrefLang="zh"/><link rel="alternate" title="在代碼中做出決定 - 條件" href="https://developer.mozilla.org/zh-TW/docs/Learn_web_development/Core/Scripting/Conditionals" hrefLang="zh-Hant"/><link rel="alternate" title="Making decisions in your code — conditionals" href="https://developer.mozilla.org/en-US/docs/Learn_web_development/Core/Scripting/Conditionals" hrefLang="en"/><link rel="preload" as="font" type="font/woff2" href="/static/media/Inter.var.c2fe3cb2b7c746f7966a.woff2" crossorigin=""/><link rel="alternate" type="application/rss+xml" title="MDN Blog RSS Feed" href="https://developer.mozilla.org/en-US/blog/rss.xml" hrefLang="en"/><meta name="description" content="In any programming language, the code needs to make decisions and carry out actions accordingly depending on different inputs. For example, in a game, if the player's number of lives is 0, then it's game over. In a weather app, if it is being looked at in the morning, show a sunrise graphic; show stars and a moon if it is nighttime. In this article, we'll explore how so-called conditional statements work in JavaScript."/><meta property="og:url" content="https://developer.mozilla.org/en-US/docs/Learn_web_development/Core/Scripting/Conditionals"/><meta property="og:title" content="Making decisions in your code — conditionals - Learn web development | MDN"/><meta property="og:type" content="website"/><meta property="og:locale" content="en_US"/><meta property="og:description" content="In any programming language, the code needs to make decisions and carry out actions accordingly depending on different inputs. For example, in a game, if the player's number of lives is 0, then it's game over. In a weather app, if it is being looked at in the morning, show a sunrise graphic; show stars and a moon if it is nighttime. 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Webpage metadata</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Headings_and_paragraphs">Headings and paragraphs in HTML</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Emphasis_and_importance">Emphasis and importance</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Lists">Lists</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Structuring_documents">Structuring documents</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Advanced_text_features">Advanced text features</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Creating_links">Creating links</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Marking_up_a_letter">Challenge: Marking up a letter</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Structuring_a_page_of_content">Challenge: Structuring a page of content</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_images">HTML images</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_video_and_audio">HTML video and audio</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Mozilla_splash_page">Challenge: Mozilla splash page</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_table_basics">HTML table basics</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Table_accessibility">HTML table accessibility</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Planet_data_table">Challenge: Structuring a planet data table</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_forms">Forms and buttons in HTML</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Debugging_HTML">Debugging HTML</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Core/Styling_basics">CSS styling basics</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/What_is_CSS">What is CSS?</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Getting_started">Getting started with CSS</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Styling_a_bio_page">Challenge: Styling a biography page</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Basic_selectors">Basic CSS selectors</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Attribute_selectors">Attribute selectors</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Pseudo_classes_and_elements">Pseudo-classes and pseudo-elements</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Combinators">Combinators</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Box_model">The box model</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Handling_conflicts">Handling conflicts</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Values_and_units">CSS values and units</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Sizing">Sizing items in CSS</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Backgrounds_and_borders">Backgrounds and borders</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Overflow">Overflowing content</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Images_media_forms">Images, media, and form elements</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Tables">Styling tables</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Debugging_CSS">Debugging CSS</a></li><li><a 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href="/en-US/docs/Learn_web_development/Core/Text_styling/Typesetting_a_homepage">Challenge: Typesetting a community school homepage</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Core/CSS_layout">CSS layout</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Introduction">Introduction to CSS layout</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Floats">Floats</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Positioning">Positioning</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Flexbox">Flexbox</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Grids">CSS grid layout</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Responsive_Design">Responsive design</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Media_queries">Media query fundamentals</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Fundamental_Layout_Comprehension">Challenge: Fundamental layout comprehension</a></li></ol></details></li><li class="toggle"><details open=""><summary><a href="/en-US/docs/Learn_web_development/Core/Scripting">Dynamic scripting with JavaScript</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/What_is_JavaScript">What is JavaScript?</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/A_first_splash">A first splash into JavaScript</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/What_went_wrong">What went wrong? Troubleshooting JavaScript</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Variables">Storing the information you need — Variables</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Math">Basic math in JavaScript — numbers and operators</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Strings">Handling text — strings in JavaScript</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Useful_string_methods">Useful string methods</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Arrays">Arrays</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Silly_story_generator">Challenge: Silly story generator</a></li><li><em><a href="/en-US/docs/Learn_web_development/Core/Scripting/Conditionals" aria-current="page">Making decisions in your code — conditionals</a></em></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Loops">Looping code</a></li><li><a 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JavaScript</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/JSON">Working with JSON</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Debugging_JavaScript">Debugging JavaScript and handling errors</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries">JavaScript frameworks and libraries</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/Introduction">Introduction to client-side frameworks</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/Main_features">Framework main features</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_getting_started">Getting started with React</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_todo_list_beginning">Beginning our React todo list</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_components">Componentizing our React app</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_events_state">React interactivity: Events and state</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_filtering_conditional_rendering">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_accessibility">Accessibility in React</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_resources">React resources</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Core/Accessibility">Accessibility</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/Accessibility/What_is_accessibility">What is accessibility?</a></li><li><a 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list and detail views</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Sessions">Django Tutorial Part 7: Sessions framework</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Authentication">Django Tutorial Part 8: User authentication and permissions</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Forms">Django Tutorial Part 9: Working with forms</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Testing">Django Tutorial Part 10: Testing a Django web application</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Deployment">Django Tutorial Part 11: Deploying Django to production</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/web_application_security">Django web application security</a></li><li><a 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href="/en-US/docs/Learn_web_development/Extensions/Performance/CSS">CSS performance optimization</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Performance/business_case_for_performance">The business case for web performance</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Extensions/Testing">Testing</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/Introduction">Introduction to cross-browser testing</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/Testing_strategies">Strategies for carrying out testing</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/HTML_and_CSS">Handling common HTML and CSS problems</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/Feature_detection">Implementing feature detection</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/Automated_testing">Introduction to automated testing</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/Your_own_automation_environment">Setting up your own test automation environment</a></li></ol></details></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Transform_animate">Transform and animate CSS</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Security_privacy">Security and privacy</a></li><li class="section">Further resources</li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Howto">How to solve common problems</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Howto/Solve_HTML_problems">Solve common HTML problems</a></li><li><a href="/en-US/docs/Learn_web_development/Howto/Solve_CSS_problems">Solve common CSS problems</a></li><li><a href="/en-US/docs/Learn_web_development/Howto/Solve_JavaScript_problems">Solve common JavaScript problems</a></li><li><a href="/en-US/docs/Learn_web_development/Howto/Web_mechanics">Web mechanics</a></li><li><a href="/en-US/docs/Learn_web_development/Howto/Tools_and_setup">Tools and setup</a></li><li><a href="/en-US/docs/Learn_web_development/Howto/Design_and_accessibility">Design and accessibility</a></li></ol></details></li><li><a href="/en-US/docs/Learn_web_development/About">About</a></li><li><a href="/en-US/docs/Learn_web_development/Educators">Resources for educators</a></li><li><a href="/en-US/docs/Learn_web_development/Changelog">Changelog</a></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="#you_can_have_it_on_one_condition!">You can have it on one condition!</a></li><li class="document-toc-item "><a class="document-toc-link" href="#if...else_statements">if...else statements</a></li><li class="document-toc-item "><a class="document-toc-link" href="#switch_statements">switch statements</a></li><li class="document-toc-item "><a class="document-toc-link" href="#ternary_operator">Ternary operator</a></li><li class="document-toc-item "><a class="document-toc-link" href="#active_learning_a_simple_calendar">Active learning: A simple calendar</a></li><li class="document-toc-item "><a class="document-toc-link" href="#active_learning_more_color_choices">Active learning: More color choices</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="#summary">Summary</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>Making decisions in your code — conditionals</h1></header><div class="section-content"><ul class="prev-next"><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Core/Scripting/Silly_story_generator"><span class="button-wrap"> Previous </span></a></li><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Core/Scripting"><span class="button-wrap"> Overview: Dynamic scripting with JavaScript</span></a></li><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Core/Scripting/Loops"><span class="button-wrap"> Next </span></a></li></ul> <p>In any programming language, the code needs to make decisions and carry out actions accordingly depending on different inputs. For example, in a game, if the player's number of lives is 0, then it's game over. In a weather app, if it is being looked at in the morning, show a sunrise graphic; show stars and a moon if it is nighttime. In this article, we'll explore how so-called conditional statements work in JavaScript.</p> <figure class="table-container"><table> <tbody> <tr> <th scope="row">Prerequisites:</th> <td>An understanding of <a href="/en-US/docs/Learn_web_development/Core/Structuring_content">HTML</a> and the <a href="/en-US/docs/Learn_web_development/Core/Styling_basics">fundamentals of CSS</a>, familiarity with JavaScript basics as covered in previous lessons.</td> </tr> <tr> <th scope="row">Learning outcomes:</th> <td> <ul> <li>Understand what a conditional is — a code structure for running different code paths depending on a test result.</li> <li>Implementing conditions using <code>if</code>/<code>else</code>/<code>else if</code>.</li> <li>Using comparison operators to create tests.</li> <li>Implementing AND, OR, and NOT logic in tests.</li> <li>Switch statements.</li> <li>Ternary operators.</li> </ul> </td> </tr> </tbody> </table></figure></div><section aria-labelledby="you_can_have_it_on_one_condition!"><h2 id="you_can_have_it_on_one_condition!"><a href="#you_can_have_it_on_one_condition!">You can have it on one condition!</a></h2><div class="section-content"><p>Human beings (and other animals) make decisions all the time that affect their lives, from small ("should I eat one cookie or two?") to large ("should I stay in my home country and work on my family's farm, or should I move to America and study astrophysics?")</p> <p>Conditional statements allow us to represent such decision making in JavaScript, from the choice that must be made (for example, "one cookie or two"), to the resulting outcome of those choices (perhaps the outcome of "ate one cookie" might be "still felt hungry", and the outcome of "ate two cookies" might be "felt full, but mom scolded me for eating all the cookies".)</p> <p><img src="/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/cookie-choice-small.png" alt="A cartoon character resembling a person holding a cookie jar labeled 'Cookies'. There is a question mark above the head of the character. There are two speech bubbles. The left speech bubble has one cookie. The right speech bubble has two cookies. Together it implies the character is trying to decide if it wants to one cookie or two cookies." width="1280" height="800" loading="lazy"></p></div></section><section aria-labelledby="if...else_statements"><h2 id="if...else_statements"><a href="#if...else_statements">if...else statements</a></h2><div class="section-content"><p>Let's look at by far the most common type of conditional statement you'll use in JavaScript — the humble <a href="/en-US/docs/Web/JavaScript/Reference/Statements/if...else"><code>if...else</code> statement</a>.</p></div></section><section aria-labelledby="basic_if...else_syntax"><h3 id="basic_if...else_syntax"><a href="#basic_if...else_syntax">Basic if...else syntax</a></h3><div class="section-content"><p>Basic <code>if...else</code> syntax looks like this:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>if (condition) { /* code to run if condition is true */ } else { /* run some other code instead */ } </code></pre></div> <p>Here we've got:</p> <ol> <li>The keyword <code>if</code> followed by some parentheses.</li> <li>A condition to test, placed inside the parentheses (typically "is this value bigger than this other value?", or "does this value exist?"). The condition makes use of the <a href="/en-US/docs/Learn_web_development/Core/Scripting/Math#comparison_operators">comparison operators</a> we discussed earlier in the module and returns <code>true</code> or <code>false</code>.</li> <li>A set of curly braces, inside which we have some code — this can be any code we like, and it only runs if the condition returns <code>true</code>.</li> <li>The keyword <code>else</code>.</li> <li>Another set of curly braces, inside which we have some more code — this can be any code we like, and it only runs if the condition is not <code>true</code> — or in other words, the condition is <code>false</code>.</li> </ol> <p>This code is pretty human-readable — it is saying "<strong>if</strong> the <strong>condition</strong> returns <code>true</code>, run code A, <strong>else</strong> run code B"</p> <p>You should note that you don't have to include the <code>else</code> and the second curly brace block — the following is also perfectly legal code:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>if (condition) { /* code to run if condition is true */ } /* run some other code */ </code></pre></div> <p>However, you need to be careful here — in this case, the second block of code is not controlled by the conditional statement, so it <strong>always</strong> runs, regardless of whether the condition returns <code>true</code> or <code>false</code>. This is not necessarily a bad thing, but it might not be what you want — often you want to run one block of code <em>or</em> the other, not both.</p> <p>As a final point, while not recommended, you may sometimes see <code>if...else</code> statements written without the curly braces:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js example-bad notranslate"><code>if (condition) /* code to run if condition is true */ else /* run some other code instead */ </code></pre></div> <p>This syntax is perfectly valid, but it is much easier to understand the code if you use the curly braces to delimit the blocks of code, and use multiple lines and indentation.</p></div></section><section aria-labelledby="a_real_example"><h3 id="a_real_example"><a href="#a_real_example">A real example</a></h3><div class="section-content"><p>To understand this syntax better, let's consider a real example. Imagine a child being asked for help with a chore by their mother or father. The parent might say "Hey sweetheart! If you help me by going and doing the shopping, I'll give you some extra allowance so you can afford that toy you wanted." In JavaScript, we could represent this like so:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>let shoppingDone = false; let childsAllowance; if (shoppingDone === true) { childsAllowance = 10; } else { childsAllowance = 5; } </code></pre></div> <p>This code as shown always results in the <code>shoppingDone</code> variable returning <code>false</code>, meaning disappointment for our poor child. It'd be up to us to provide a mechanism for the parent to set the <code>shoppingDone</code> variable to <code>true</code> if the child did the shopping.</p> <div class="notecard note"> <p><strong>Note:</strong> You can see a more <a href="https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/allowance-updater.html" class="external" target="_blank">complete version of this example on GitHub</a> (also see it <a href="https://mdn.github.io/learning-area/javascript/building-blocks/allowance-updater.html" class="external" target="_blank">running live</a>.)</p> </div></div></section><section aria-labelledby="else_if"><h3 id="else_if"><a href="#else_if">else if</a></h3><div class="section-content"><p>The last example provided us with two choices, or outcomes — but what if we want more than two?</p> <p>There is a way to chain on extra choices/outcomes to your <code>if...else</code> — using <code>else if</code>. Each extra choice requires an additional block to put in between <code>if () { }</code> and <code>else { }</code> — check out the following more involved example, which could be part of a simple weather forecast application:</p> <div class="code-example"><div class="example-header"><span class="language-name">html</span></div><pre class="brush: html notranslate"><code><label for="weather">Select the weather type today: </label> <select id="weather"> <option value="">--Make a choice--</option> <option value="sunny">Sunny</option> <option value="rainy">Rainy</option> <option value="snowing">Snowing</option> <option value="overcast">Overcast</option> </select> <p></p> </code></pre></div> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const select = document.querySelector("select"); const para = document.querySelector("p"); select.addEventListener("change", setWeather); function setWeather() { const choice = select.value; if (choice === "sunny") { para.textContent = "It is nice and sunny outside today. Wear shorts! Go to the beach, or the park, and get an ice cream."; } else if (choice === "rainy") { para.textContent = "Rain is falling outside; take a rain coat and an umbrella, and don't stay out for too long."; } else if (choice === "snowing") { para.textContent = "The snow is coming down — it is freezing! Best to stay in with a cup of hot chocolate, or go build a snowman."; } else if (choice === "overcast") { para.textContent = "It isn't raining, but the sky is grey and gloomy; it could turn any minute, so take a rain coat just in case."; } else { para.textContent = ""; } } </code></pre></div> <div class="code-example"><div class="example-header"></div><iframe class="sample-code-frame" title="else if sample" id="frame_else_if" width="100%" height="100" src="about:blank" data-live-path="/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/" data-live-id="else_if" sandbox="allow-same-origin allow-scripts" loading="lazy"></iframe></div> <ol> <li>Here we've got an HTML <a href="/en-US/docs/Web/HTML/Element/select"><code><select></code></a> element allowing us to make different weather choices, and a simple paragraph.</li> <li>In the JavaScript, we are storing a reference to both the <a href="/en-US/docs/Web/HTML/Element/select"><code><select></code></a> and <a href="/en-US/docs/Web/HTML/Element/p"><code><p></code></a> elements, and adding an event listener to the <code><select></code> element so that when its value is changed, the <code>setWeather()</code> function is run.</li> <li>When this function is run, we first set a variable called <code>choice</code> to the current value selected in the <code><select></code> element. We then use a conditional statement to show different text inside the paragraph depending on what the value of <code>choice</code> is. Notice how all the conditions are tested in <code>else if () { }</code> blocks, except for the first one, which is tested in an <code>if () { }</code> block.</li> <li>The very last choice, inside the <code>else { }</code> block, is basically a "last resort" option — the code inside it will be run if none of the conditions are <code>true</code>. In this case, it serves to empty the text out of the paragraph if nothing is selected, for example, if a user decides to re-select the "--Make a choice--" placeholder option shown at the beginning.</li> </ol> <div class="notecard note"> <p><strong>Note:</strong> You can also <a href="https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/simple-else-if.html" class="external" target="_blank">find this example on GitHub</a> (<a href="https://mdn.github.io/learning-area/javascript/building-blocks/simple-else-if.html" class="external" target="_blank">see it running live</a> on there also.)</p> </div></div></section><section aria-labelledby="a_note_on_comparison_operators"><h3 id="a_note_on_comparison_operators"><a href="#a_note_on_comparison_operators">A note on comparison operators</a></h3><div class="section-content"><p>Comparison operators are used to test the conditions inside our conditional statements. We first looked at comparison operators back in our <a href="/en-US/docs/Learn_web_development/Core/Scripting/Math#comparison_operators">Basic math in JavaScript — numbers and operators</a> article. Our choices are:</p> <ul> <li><code>===</code> and <code>!==</code> — test if one value is identical to, or not identical to, another.</li> <li><code><</code> and <code>></code> — test if one value is less than or greater than another.</li> <li><code><=</code> and <code>>=</code> — test if one value is less than or equal to, or greater than or equal to, another.</li> </ul> <p>We wanted to make a special mention of testing boolean (<code>true</code>/<code>false</code>) values, and a common pattern you'll come across again and again. Any value that is not <code>false</code>, <code>undefined</code>, <code>null</code>, <code>0</code>, <code>NaN</code>, or an empty string (<code>''</code>) actually returns <code>true</code> when tested as a conditional statement, therefore you can use a variable name on its own to test whether it is <code>true</code>, or even that it exists (that is, it is not undefined.) So for example:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>let cheese = "Cheddar"; if (cheese) { console.log("Yay! Cheese available for making cheese on toast."); } else { console.log("No cheese on toast for you today."); } </code></pre></div> <p>And, returning to our previous example about the child doing a chore for their parent, you could write it like this:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>let shoppingDone = false; let childsAllowance; // We don't need to explicitly specify 'shoppingDone === true' if (shoppingDone) { childsAllowance = 10; } else { childsAllowance = 5; } </code></pre></div></div></section><section aria-labelledby="nesting_if...else"><h3 id="nesting_if...else"><a href="#nesting_if...else">Nesting if...else</a></h3><div class="section-content"><p>It is perfectly OK to put one <code>if...else</code> statement inside another one — to nest them. For example, we could update our weather forecast application to show a further set of choices depending on what the temperature is:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>if (choice === "sunny") { if (temperature < 86) { para.textContent = `It is ${temperature} degrees outside — nice and sunny. Let's go out to the beach, or the park, and get an ice cream.`; } else if (temperature >= 86) { para.textContent = `It is ${temperature} degrees outside — REALLY HOT! If you want to go outside, make sure to put some sunscreen on.`; } } </code></pre></div> <p>Even though the code all works together, each <code>if...else</code> statement works completely independently of the other one.</p></div></section><section aria-labelledby="logical_operators_and_or_and_not"><h3 id="logical_operators_and_or_and_not"><a href="#logical_operators_and_or_and_not">Logical operators: AND, OR and NOT</a></h3><div class="section-content"><p>If you want to test multiple conditions without writing nested <code>if...else</code> statements, <a href="/en-US/docs/Web/JavaScript/Reference/Operators">logical operators</a> can help you. When used in conditions, the first two do the following:</p> <ul> <li><code>&&</code> — AND; allows you to chain together two or more expressions so that all of them have to individually evaluate to <code>true</code> for the whole expression to return <code>true</code>.</li> <li><code>||</code> — OR; allows you to chain together two or more expressions so that one or more of them have to individually evaluate to <code>true</code> for the whole expression to return <code>true</code>.</li> </ul> <p>To give you an AND example, the previous example snippet can be rewritten to this:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>if (choice === "sunny" && temperature < 86) { para.textContent = `It is ${temperature} degrees outside — nice and sunny. Let's go out to the beach, or the park, and get an ice cream.`; } else if (choice === "sunny" && temperature >= 86) { para.textContent = `It is ${temperature} degrees outside — REALLY HOT! If you want to go outside, make sure to put some sunscreen on.`; } </code></pre></div> <p>So for example, the first code block will only be run if <code>choice === 'sunny'</code> <em>and</em> <code>temperature < 86</code> return <code>true</code>.</p> <p>Let's look at a quick OR example:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>if (iceCreamVanOutside || houseStatus === "on fire") { console.log("You should leave the house quickly."); } else { console.log("Probably should just stay in then."); } </code></pre></div> <p>The last type of logical operator, NOT, expressed by the <code>!</code> operator, can be used to negate an expression. Let's combine it with OR in the above example:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>if (!(iceCreamVanOutside || houseStatus === "on fire")) { console.log("Probably should just stay in then."); } else { console.log("You should leave the house quickly."); } </code></pre></div> <p>In this snippet, if the OR statement returns <code>true</code>, the NOT operator will negate it so that the overall expression returns <code>false</code>.</p> <p>You can combine as many logical statements together as you want, in whatever structure. The following example executes the code inside only if both OR statements return true, meaning that the overall AND statement will return true:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>if ((x === 5 || y > 3 || z <= 10) && (loggedIn || userName === "Steve")) { // run the code } </code></pre></div> <p>A common mistake when using the logical OR operator in conditional statements is to try to state the variable whose value you are checking once, and then give a list of values it could be to return true, separated by <code>||</code> (OR) operators. For example:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js example-bad notranslate"><code>if (x === 5 || 7 || 10 || 20) { // run my code } </code></pre></div> <p>In this case, the condition inside <code>if ()</code> will always evaluate to true since 7 (or any other non-zero value) always evaluates to <code>true</code>. This condition is actually saying "if x equals 5, or 7 is true — which it always is". This is logically not what we want! To make this work you've got to specify a complete test on either side of each OR operator:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>if (x === 5 || x === 7 || x === 10 || x === 20) { // run my code } </code></pre></div></div></section><section aria-labelledby="switch_statements"><h2 id="switch_statements"><a href="#switch_statements">switch statements</a></h2><div class="section-content"><p><code>if...else</code> statements do the job of enabling conditional code well, but they are not without their downsides. They are mainly good for cases where you've got a couple of choices, and each one requires a reasonable amount of code to be run, and/or the conditions are complex (for example, multiple logical operators). For cases where you just want to set a variable to a certain choice of value or print out a particular statement depending on a condition, the syntax can be a bit cumbersome, especially if you've got a large number of choices.</p> <p>In such a case, <a href="/en-US/docs/Web/JavaScript/Reference/Statements/switch"><code>switch</code> statements</a> are your friend — they take a single expression/value as an input, and then look through several choices until they find one that matches that value, executing the corresponding code that goes along with it. Here's some more pseudocode, to give you an idea:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>switch (expression) { case choice1: // run this code break; case choice2: // run this code instead break; // include as many cases as you like default: // actually, just run this code break; } </code></pre></div> <p>Here we've got:</p> <ol> <li>The keyword <code>switch</code>, followed by a set of parentheses.</li> <li>An expression or value inside the parentheses.</li> <li>The keyword <code>case</code>, followed by a choice that the expression/value could be, followed by a colon.</li> <li>Some code to run if the choice matches the expression.</li> <li>A <code>break</code> statement, followed by a semicolon. If the previous choice matches the expression/value, the browser stops executing the code block here, and moves on to any code that appears below the switch statement.</li> <li>As many other cases (bullets 3–5) as you like.</li> <li>The keyword <code>default</code>, followed by exactly the same code pattern as one of the cases (bullets 3–5), except that <code>default</code> does not have a choice after it, and you don't need the <code>break</code> statement as there is nothing to run after this in the block anyway. This is the default option that runs if none of the choices match.</li> </ol> <div class="notecard note"> <p><strong>Note:</strong> You don't have to include the <code>default</code> section — you can safely omit it if there is no chance that the expression could end up equaling an unknown value. If there is a chance of this, however, you need to include it to handle unknown cases.</p> </div></div></section><section aria-labelledby="a_switch_example"><h3 id="a_switch_example"><a href="#a_switch_example">A switch example</a></h3><div class="section-content"><p>Let's have a look at a real example — we'll rewrite our weather forecast application to use a switch statement instead:</p> <div class="code-example"><div class="example-header"><span class="language-name">html</span></div><pre class="brush: html notranslate"><code><label for="weather">Select the weather type today: </label> <select id="weather"> <option value="">--Make a choice--</option> <option value="sunny">Sunny</option> <option value="rainy">Rainy</option> <option value="snowing">Snowing</option> <option value="overcast">Overcast</option> </select> <p></p> </code></pre></div> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const select = document.querySelector("select"); const para = document.querySelector("p"); select.addEventListener("change", setWeather); function setWeather() { const choice = select.value; switch (choice) { case "sunny": para.textContent = "It is nice and sunny outside today. Wear shorts! Go to the beach, or the park, and get an ice cream."; break; case "rainy": para.textContent = "Rain is falling outside; take a rain coat and an umbrella, and don't stay out for too long."; break; case "snowing": para.textContent = "The snow is coming down — it is freezing! Best to stay in with a cup of hot chocolate, or go build a snowman."; break; case "overcast": para.textContent = "It isn't raining, but the sky is grey and gloomy; it could turn any minute, so take a rain coat just in case."; break; default: para.textContent = ""; } } </code></pre></div> <div class="code-example"><div class="example-header"></div><iframe class="sample-code-frame" title="A switch example sample" id="frame_a_switch_example" width="100%" height="100" src="about:blank" data-live-path="/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/" data-live-id="a_switch_example" sandbox="allow-same-origin allow-scripts" loading="lazy"></iframe></div> <div class="notecard note"> <p><strong>Note:</strong> You can also <a href="https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/simple-switch.html" class="external" target="_blank">find this example on GitHub</a> (see it <a href="https://mdn.github.io/learning-area/javascript/building-blocks/simple-switch.html" class="external" target="_blank">running live</a> on there also.)</p> </div></div></section><section aria-labelledby="ternary_operator"><h2 id="ternary_operator"><a href="#ternary_operator">Ternary operator</a></h2><div class="section-content"><p>There is one final bit of syntax we want to introduce you to before we get you to play with some examples. The <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_operator">ternary or conditional operator</a> is a small bit of syntax that tests a condition and returns one value/expression if it is <code>true</code>, and another if it is <code>false</code> — this can be useful in some situations, and can take up a lot less code than an <code>if...else</code> block if you have two choices that are chosen between via a <code>true</code>/<code>false</code> condition. The pseudocode looks like this:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>condition ? run this code : run this code instead </code></pre></div> <p>So let's look at an example:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const greeting = isBirthday ? "Happy birthday Mrs. Smith — we hope you have a great day!" : "Good morning Mrs. Smith."; </code></pre></div> <p>Here we have a variable called <code>isBirthday</code> — if this is <code>true</code>, we give our guest a happy birthday message; if not, we give her the standard daily greeting.</p></div></section><section aria-labelledby="ternary_operator_example"><h3 id="ternary_operator_example"><a href="#ternary_operator_example">Ternary operator example</a></h3><div class="section-content"><p>The ternary operator is not just for setting variable values; you can also run functions, or lines of code — anything you like. The following live example shows a simple theme chooser where the styling for the site is applied using a ternary operator.</p> <div class="code-example"><div class="example-header"><span class="language-name">html</span></div><pre class="brush: html notranslate"><code><label for="theme">Select theme: </label> <select id="theme"> <option value="white">White</option> <option value="black">Black</option> </select> <h1>This is my website</h1> </code></pre></div> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const select = document.querySelector("select"); const html = document.querySelector("html"); document.body.style.padding = "10px"; function update(bgColor, textColor) { html.style.backgroundColor = bgColor; html.style.color = textColor; } select.addEventListener("change", () => select.value === "black" ? update("black", "white") : update("white", "black"), ); </code></pre></div> <div class="code-example"><div class="example-header"></div><iframe class="sample-code-frame" title="Ternary operator example sample" id="frame_ternary_operator_example" width="100%" height="300" src="about:blank" data-live-path="/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/" data-live-id="ternary_operator_example" sandbox="allow-same-origin allow-scripts" loading="lazy"></iframe></div> <p>Here we've got a <a href="/en-US/docs/Web/HTML/Element/select"><code><select></code></a> element to choose a theme (black or white), plus a simple <a href="/en-US/docs/Web/HTML/Element/Heading_Elements">h1</a> to display a website title. We also have a function called <code>update()</code>, which takes two colors as parameters (inputs). The website's background color is set to the first provided color, and its text color is set to the second provided color.</p> <p>Finally, we've also got an <a href="/en-US/docs/Web/API/HTMLElement/change_event">onchange</a> event listener that serves to run a function containing a ternary operator. It starts with a test condition — <code>select.value === 'black'</code>. If this returns <code>true</code>, we run the <code>update()</code> function with parameters of black and white, meaning that we end up with a background color of black and a text color of white. If it returns <code>false</code>, we run the <code>update()</code> function with parameters of white and black, meaning that the site colors are inverted.</p> <div class="notecard note"> <p><strong>Note:</strong> You can also <a href="https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/simple-ternary.html" class="external" target="_blank">find this example on GitHub</a> (see it <a href="https://mdn.github.io/learning-area/javascript/building-blocks/simple-ternary.html" class="external" target="_blank">running live</a> on there also.)</p> </div></div></section><section aria-labelledby="active_learning_a_simple_calendar"><h2 id="active_learning_a_simple_calendar"><a href="#active_learning_a_simple_calendar">Active learning: A simple calendar</a></h2><div class="section-content"><p>In this example, you are going to help us finish a simple calendar application. In the code you've got:</p> <ul> <li>A <a href="/en-US/docs/Web/HTML/Element/select"><code><select></code></a> element to allow the user to choose between different months.</li> <li>An <code>onchange</code> event handler to detect when the value selected in the <code><select></code> menu is changed.</li> <li>A function called <code>createCalendar()</code> that draws the calendar and displays the correct month in the <a href="/en-US/docs/Web/HTML/Element/Heading_Elements">h1</a> element.</li> </ul> <p>We need you to write a conditional statement inside the <code>createCalendar()</code> function, just below the <code>// ADD CONDITIONAL HERE</code> comment. It should:</p> <ol> <li>Look at the selected month (stored in the <code>choice</code> variable. This will be the <code><select></code> element value after the value changes, so "January" for example.)</li> <li>Assign the <code>days</code> variable to be equal to the number of days in the selected month. To do this you'll have to look up the number of days in each month of the year. You can ignore leap years for the purposes of this example.</li> </ol> <p>Hints:</p> <ul> <li>You are advised to use logical OR to group multiple months together into a single condition; many of them share the same number of days.</li> <li>Think about which number of days is the most common, and use that as a default value.</li> </ul> <p>If you make a mistake, you can always reset the example with the "Reset" button. If you get really stuck, press "Show solution" to see a solution.</p> <div class="code-example"><pre class="brush: html hidden notranslate"><code><h2>Live output</h2> <iframe id="output" width="100%" height="600px"></iframe> <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: 400px;width: 95%"> const select = document.querySelector("select"); const list = document.querySelector("ul"); const h1 = document.querySelector("h1"); select.addEventListener("change", () => { const choice = select.value; createCalendar(choice); }); function createCalendar(month) { let days = 31; // ADD CONDITIONAL HERE list.textContent = ""; h1.textContent = month; for (let i = 1; i <= days; i++) { const listItem = document.createElement("li"); listItem.textContent = i; list.appendChild(listItem); } } select.value = "January"; createCalendar("January"); </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 reset = document.getElementById("reset"); const solution = document.getElementById("solution"); const outputIFrame = document.querySelector("#output"); const textarea = document.getElementById("code"); const initialCode = textarea.value; let userCode = textarea.value; const solutionCode = `const select = document.querySelector("select"); const list = document.querySelector("ul"); const h1 = document.querySelector("h1"); select.addEventListener("change", () => { const choice = select.value; createCalendar(choice); }); function createCalendar(month) { let days = 31; if (month === "February") { days = 28; } else if ( month === "April" || month === "June" || month === "September" || month === "November" ) { days = 30; } list.textContent = ""; h1.textContent = month; for (let i = 1; i <= days; i++) { const listItem = document.createElement("li"); listItem.textContent = i; list.appendChild(listItem); } } select.value = "January"; createCalendar("January");`; function outputDocument(code) { const outputBody = ` <div class="output" style="height: 500px; overflow: auto"> <label for="month">Select month: </label> <select id="month"> <option value="January">January</option> <option value="February">February</option> <option value="March">March</option> <option value="April">April</option> <option value="May">May</option> <option value="June">June</option> <option value="July">July</option> <option value="August">August</option> <option value="September">September</option> <option value="October">October</option> <option value="November">November</option> <option value="December">December</option> </select> <h1></h1> <ul></ul> </div>`; const outputStyle = ` .output * { box-sizing: border-box; } .output ul { padding-left: 0; } .output li { display: block; float: left; width: 25%; border: 2px solid white; padding: 5px; height: 40px; background-color: #4a2db6; color: white; } html { font-family: sans-serif; } h2 { font-size: 16px; }`; return ` <!doctype html> <html> <head> <style>${outputStyle}</style> </head> <body> ${outputBody} <script>${code}<${"/"}script> </body> </html>`; } function update() { output.setAttribute("srcdoc", outputDocument(textarea.value)); } update(); textarea.addEventListener("input", update); reset.addEventListener("click", () => { textarea.value = initialCode; userEntry = textarea.value; solution.value = "Show solution"; update(); }); solution.addEventListener("click", () => { if (solution.value === "Show solution") { // remember the state of the user's code // so we can restore it userCode = textarea.value; textarea.value = solutionCode; solution.value = "Hide solution"; } else { textarea.value = userCode; solution.value = "Show solution"; } update(); }); // stop tab key tabbing out of textarea and // make it write a tab at the caret position instead textarea.onkeydown = (e) => { if (e.code === "Tab") { e.preventDefault(); insertAtCaret("\t"); } if (e.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; } </code></pre></div> <div class="code-example"><div class="example-header"></div><iframe class="sample-code-frame" title="Active learning A simple calendar sample" id="frame_active_learning_a_simple_calendar" width="100%" height="1210" src="about:blank" data-live-path="/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/" data-live-id="active_learning_a_simple_calendar" sandbox="allow-same-origin allow-scripts" loading="lazy"></iframe></div></div></section><section aria-labelledby="active_learning_more_color_choices"><h2 id="active_learning_more_color_choices"><a href="#active_learning_more_color_choices">Active learning: More color choices</a></h2><div class="section-content"><p>In this example, you are going to take the ternary operator example we saw earlier and convert the ternary operator into a switch statement to allow us to apply more choices to the simple website. Look at the <a href="/en-US/docs/Web/HTML/Element/select"><code><select></code></a> — this time you'll see that it has not two theme options, but five. You need to add a switch statement just underneath the <code>// ADD SWITCH STATEMENT</code> comment:</p> <ul> <li>It should accept the <code>choice</code> variable as its input expression.</li> <li>For each case, the choice should equal one of the possible <code><option></code> values that can be selected, that is, <code>white</code>, <code>black</code>, <code>purple</code>, <code>yellow</code>, or <code>psychedelic</code>. Note that the option values are lowercase, while the option <em>labels</em>, as displayed in the live output, are capitalized. You should use the lowercase values in your code.</li> <li>For each case, the <code>update()</code> function should be run, and be passed two color values, the first one for the background color, and the second one for the text color. Remember that color values are strings, so they need to be wrapped in quotes.</li> </ul> <p>If you make a mistake, you can always reset the example with the "Reset" button. If you get really stuck, press "Show solution" to see a solution.</p> <div class="code-example"><pre class="brush: html hidden notranslate"><code><h2>Live output</h2> <iframe id="output" width="100%" height="350px"></iframe> <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: 400px;width: 95%"> const select = document.querySelector('select'); const html = document.querySelector('.output'); select.addEventListener('change', () => { const choice = select.value; // ADD SWITCH STATEMENT }); function update(bgColor, textColor) { html.style.backgroundColor = bgColor; html.style.color = textColor; } </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 reset = document.getElementById("reset"); const solution = document.getElementById("solution"); const outputIFrame = document.querySelector("#output"); const textarea = document.getElementById("code"); const initialCode = textarea.value; let userCode = textarea.value; const solutionCode = `const select = document.querySelector('select'); const html = document.querySelector('.output'); select.addEventListener('change', () => { const choice = select.value; switch(choice) { case 'black': update('black','white'); break; case 'white': update('white','black'); break; case 'purple': update('purple','white'); break; case 'yellow': update('yellow','purple'); break; case 'psychedelic': update('lime','purple'); break; } }); function update(bgColor, textColor) { html.style.backgroundColor = bgColor; html.style.color = textColor; }`; function outputDocument(code) { const outputBody = ` <div class="output" style="height: 300px;"> <label for="theme">Select theme: </label> <select id="theme"> <option value="white">White</option> <option value="black">Black</option> <option value="purple">Purple</option> <option value="yellow">Yellow</option> <option value="psychedelic">Psychedelic</option> </select> <h1>This is my website</h1> </div>`; return ` <!doctype html> <html> <head> </head> <body> ${outputBody} <script>${code}<${"/"}script> </body> </html>`; } function update() { output.setAttribute("srcdoc", outputDocument(textarea.value)); } update(); textarea.addEventListener("input", update); reset.addEventListener("click", () => { textarea.value = initialCode; userEntry = textarea.value; solution.value = "Show solution"; update(); }); solution.addEventListener("click", () => { if (solution.value === "Show solution") { // remember the state of the user's code // so we can restore it userCode = textarea.value; textarea.value = solutionCode; solution.value = "Hide solution"; } else { textarea.value = userCode; solution.value = "Show solution"; } update(); }); // stop tab key tabbing out of textarea and // make it write a tab at the caret position instead textarea.onkeydown = (e) => { if (e.code === "Tab") { e.preventDefault(); insertAtCaret("\t"); } if (e.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; } </code></pre></div> <div class="code-example"><div class="example-header"></div><iframe class="sample-code-frame" title="Active learning More color choices sample" id="frame_active_learning_more_color_choices" width="100%" height="950" src="about:blank" data-live-path="/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/" data-live-id="active_learning_more_color_choices" 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_web_development/Core/Scripting/Test_your_skills:_Conditionals">Test your skills: Conditionals</a>.</p></div></section><section aria-labelledby="summary"><h2 id="summary"><a href="#summary">Summary</a></h2><div class="section-content"><p>That's all you really need to know about conditional structures in JavaScript right now! Next up, we'll look at looping through code.</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/Learn_web_development/Core/Scripting/Math#comparison_operators">Comparison operators</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Control_flow_and_error_handling#conditional_statements">Conditional statements in detail</a></li> <li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/if...else">if...else reference</a></li> <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_operator">Conditional (ternary) operator reference</a></li> </ul> <ul class="prev-next"><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Core/Scripting/Silly_story_generator"><span class="button-wrap"> Previous </span></a></li><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Core/Scripting"><span class="button-wrap"> Overview: Dynamic scripting with JavaScript</span></a></li><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Core/Scripting/Loops"><span class="button-wrap"> Next </span></a></li></ul></div></section></article><aside class="article-footer"><div class="article-footer-inner"><div class="svg-container"><svg xmlns="http://www.w3.org/2000/svg" width="162" height="162" viewBox="0 0 162 162" fill="none" role="none"><mask id="b" fill="#fff"><path d="M97.203 47.04c8.113-7.886 18.004-13.871 28.906-17.492a78 78 0 0 1 33.969-3.39c11.443 1.39 22.401 5.295 32.024 11.411s17.656 14.28 23.476 23.86c5.819 9.579 9.269 20.318 10.083 31.385a69.85 69.85 0 0 1-5.387 32.44c-4.358 10.272-11.115 19.443-19.747 26.801-8.632 7.359-18.908 12.709-30.034 15.637l-6.17-21.698c7.666-2.017 14.746-5.703 20.694-10.773 5.948-5.071 10.603-11.389 13.606-18.467a48.14 48.14 0 0 0 3.712-22.352c-.561-7.625-2.938-15.025-6.948-21.625s-9.544-12.226-16.175-16.44-14.181-6.904-22.065-7.863a53.75 53.75 0 0 0-23.405 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class="footer-moz-link" target="_blank" rel="noopener noreferrer">Cookies</a></li><li class="footer-moz-item"><a href="https://www.mozilla.org/about/legal/terms/mozilla" class="footer-moz-link" target="_blank" rel="noopener noreferrer">Legal</a></li><li class="footer-moz-item"><a href="https://www.mozilla.org/about/governance/policies/participation/" class="footer-moz-link" target="_blank" rel="noopener noreferrer">Community Participation Guidelines</a></li></ul></div><div class="page-footer-legal"><p id="license" class="page-footer-legal-text">Visit <a href="https://www.mozilla.org" target="_blank" rel="noopener noreferrer">Mozilla Corporation’s</a> not-for-profit parent, the <a target="_blank" rel="noopener noreferrer" href="https://foundation.mozilla.org/">Mozilla Foundation</a>.<br/>Portions of this content are ©1998–2025 by individual mozilla.org contributors. 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_web_development/Core/Scripting/Conditionals","doc":{"body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<ul class=\"prev-next\"><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Core/Scripting/Silly_story_generator\"><span class=\"button-wrap\"> Previous </span></a></li><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Core/Scripting\"><span class=\"button-wrap\"> Overview: Dynamic scripting with JavaScript</span></a></li><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Core/Scripting/Loops\"><span class=\"button-wrap\"> Next </span></a></li></ul>\n<p>In any programming language, the code needs to make decisions and carry out actions accordingly depending on different inputs. For example, in a game, if the player's number of lives is 0, then it's game over. In a weather app, if it is being looked at in the morning, show a sunrise graphic; show stars and a moon if it is nighttime. In this article, we'll explore how so-called conditional statements work in JavaScript.</p>\n<figure class=\"table-container\"><table>\n <tbody>\n <tr>\n <th scope=\"row\">Prerequisites:</th>\n <td>An understanding of <a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content\">HTML</a> and the <a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics\">fundamentals of CSS</a>, familiarity with JavaScript basics as covered in previous lessons.</td>\n </tr>\n <tr>\n <th scope=\"row\">Learning outcomes:</th>\n <td>\n <ul>\n <li>Understand what a conditional is — a code structure for running different code paths depending on a test result.</li>\n <li>Implementing conditions using <code>if</code>/<code>else</code>/<code>else if</code>.</li>\n <li>Using comparison operators to create tests.</li>\n <li>Implementing AND, OR, and NOT logic in tests.</li>\n <li>Switch statements.</li>\n <li>Ternary operators.</li>\n </ul>\n </td>\n </tr>\n </tbody>\n</table></figure>"}},{"type":"prose","value":{"id":"you_can_have_it_on_one_condition!","title":"You can have it on one condition!","isH3":false,"content":"<p>Human beings (and other animals) make decisions all the time that affect their lives, from small (\"should I eat one cookie or two?\") to large (\"should I stay in my home country and work on my family's farm, or should I move to America and study astrophysics?\")</p>\n<p>Conditional statements allow us to represent such decision making in JavaScript, from the choice that must be made (for example, \"one cookie or two\"), to the resulting outcome of those choices (perhaps the outcome of \"ate one cookie\" might be \"still felt hungry\", and the outcome of \"ate two cookies\" might be \"felt full, but mom scolded me for eating all the cookies\".)</p>\n<p><img src=\"/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/cookie-choice-small.png\" alt=\"A cartoon character resembling a person holding a cookie jar labeled 'Cookies'. There is a question mark above the head of the character. There are two speech bubbles. The left speech bubble has one cookie. The right speech bubble has two cookies. Together it implies the character is trying to decide if it wants to one cookie or two cookies.\" width=\"1280\" height=\"800\" loading=\"lazy\"></p>"}},{"type":"prose","value":{"id":"if...else_statements","title":"if...else statements","isH3":false,"content":"<p>Let's look at by far the most common type of conditional statement you'll use in JavaScript — the humble <a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/if...else\"><code>if...else</code> statement</a>.</p>"}},{"type":"prose","value":{"id":"basic_if...else_syntax","title":"Basic if...else syntax","isH3":true,"content":"<p>Basic <code>if...else</code> syntax looks 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>if (condition) {\n /* code to run if condition is true */\n} else {\n /* run some other code instead */\n}\n</code></pre></div>\n<p>Here we've got:</p>\n<ol>\n<li>The keyword <code>if</code> followed by some parentheses.</li>\n<li>A condition to test, placed inside the parentheses (typically \"is this value bigger than this other value?\", or \"does this value exist?\"). The condition makes use of the <a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Math#comparison_operators\">comparison operators</a> we discussed earlier in the module and returns <code>true</code> or <code>false</code>.</li>\n<li>A set of curly braces, inside which we have some code — this can be any code we like, and it only runs if the condition returns <code>true</code>.</li>\n<li>The keyword <code>else</code>.</li>\n<li>Another set of curly braces, inside which we have some more code — this can be any code we like, and it only runs if the condition is not <code>true</code> — or in other words, the condition is <code>false</code>.</li>\n</ol>\n<p>This code is pretty human-readable — it is saying \"<strong>if</strong> the <strong>condition</strong> returns <code>true</code>, run code A, <strong>else</strong> run code B\"</p>\n<p>You should note that you don't have to include the <code>else</code> and the second curly brace block — the following is also perfectly legal code:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>if (condition) {\n /* code to run if condition is true */\n}\n\n/* run some other code */\n</code></pre></div>\n<p>However, you need to be careful here — in this case, the second block of code is not controlled by the conditional statement, so it <strong>always</strong> runs, regardless of whether the condition returns <code>true</code> or <code>false</code>. This is not necessarily a bad thing, but it might not be what you want — often you want to run one block of code <em>or</em> the other, not both.</p>\n<p>As a final point, while not recommended, you may sometimes see <code>if...else</code> statements written without the curly braces:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js example-bad notranslate\"><code>if (condition) /* code to run if condition is true */\nelse /* run some other code instead */\n</code></pre></div>\n<p>This syntax is perfectly valid, but it is much easier to understand the code if you use the curly braces to delimit the blocks of code, and use multiple lines and indentation.</p>"}},{"type":"prose","value":{"id":"a_real_example","title":"A real example","isH3":true,"content":"<p>To understand this syntax better, let's consider a real example. Imagine a child being asked for help with a chore by their mother or father. The parent might say \"Hey sweetheart! If you help me by going and doing the shopping, I'll give you some extra allowance so you can afford that toy you wanted.\" In JavaScript, we could represent this like so:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>let shoppingDone = false;\nlet childsAllowance;\n\nif (shoppingDone === true) {\n childsAllowance = 10;\n} else {\n childsAllowance = 5;\n}\n</code></pre></div>\n<p>This code as shown always results in the <code>shoppingDone</code> variable returning <code>false</code>, meaning disappointment for our poor child. It'd be up to us to provide a mechanism for the parent to set the <code>shoppingDone</code> variable to <code>true</code> if the child did the shopping.</p>\n<div class=\"notecard note\">\n<p><strong>Note:</strong>\nYou can see a more <a href=\"https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/allowance-updater.html\" class=\"external\" target=\"_blank\">complete version of this example on GitHub</a> (also see it <a href=\"https://mdn.github.io/learning-area/javascript/building-blocks/allowance-updater.html\" class=\"external\" target=\"_blank\">running live</a>.)</p>\n</div>"}},{"type":"prose","value":{"id":"else_if","title":"else if","isH3":true,"content":"<p>The last example provided us with two choices, or outcomes — but what if we want more than two?</p>\n<p>There is a way to chain on extra choices/outcomes to your <code>if...else</code> — using <code>else if</code>. Each extra choice requires an additional block to put in between <code>if () { }</code> and <code>else { }</code> — check out the following more involved example, which could be part of a simple weather forecast application:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">html</span></div><pre class=\"brush: html notranslate\"><code><label for=\"weather\">Select the weather type today: </label>\n<select id=\"weather\">\n <option value=\"\">--Make a choice--</option>\n <option value=\"sunny\">Sunny</option>\n <option value=\"rainy\">Rainy</option>\n <option value=\"snowing\">Snowing</option>\n <option value=\"overcast\">Overcast</option>\n</select>\n\n<p></p>\n</code></pre></div>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const select = document.querySelector(\"select\");\nconst para = document.querySelector(\"p\");\n\nselect.addEventListener(\"change\", setWeather);\n\nfunction setWeather() {\n const choice = select.value;\n\n if (choice === \"sunny\") {\n para.textContent =\n \"It is nice and sunny outside today. Wear shorts! Go to the beach, or the park, and get an ice cream.\";\n } else if (choice === \"rainy\") {\n para.textContent =\n \"Rain is falling outside; take a rain coat and an umbrella, and don't stay out for too long.\";\n } else if (choice === \"snowing\") {\n para.textContent =\n \"The snow is coming down — it is freezing! Best to stay in with a cup of hot chocolate, or go build a snowman.\";\n } else if (choice === \"overcast\") {\n para.textContent =\n \"It isn't raining, but the sky is grey and gloomy; it could turn any minute, so take a rain coat just in case.\";\n } else {\n para.textContent = \"\";\n }\n}\n</code></pre></div>\n<div class=\"code-example\"><div class=\"example-header\"></div><iframe class=\"sample-code-frame\" title=\"else if sample\" id=\"frame_else_if\" width=\"100%\" height=\"100\" src=\"about:blank\" data-live-path=\"/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/\" data-live-id=\"else_if\" sandbox=\"allow-same-origin allow-scripts\" loading=\"lazy\"></iframe></div>\n<ol>\n<li>Here we've got an HTML <a href=\"/en-US/docs/Web/HTML/Element/select\"><code><select></code></a> element allowing us to make different weather choices, and a simple paragraph.</li>\n<li>In the JavaScript, we are storing a reference to both the <a href=\"/en-US/docs/Web/HTML/Element/select\"><code><select></code></a> and <a href=\"/en-US/docs/Web/HTML/Element/p\"><code><p></code></a> elements, and adding an event listener to the <code><select></code> element so that when its value is changed, the <code>setWeather()</code> function is run.</li>\n<li>When this function is run, we first set a variable called <code>choice</code> to the current value selected in the <code><select></code> element. We then use a conditional statement to show different text inside the paragraph depending on what the value of <code>choice</code> is. Notice how all the conditions are tested in <code>else if () { }</code> blocks, except for the first one, which is tested in an <code>if () { }</code> block.</li>\n<li>The very last choice, inside the <code>else { }</code> block, is basically a \"last resort\" option — the code inside it will be run if none of the conditions are <code>true</code>. In this case, it serves to empty the text out of the paragraph if nothing is selected, for example, if a user decides to re-select the \"--Make a choice--\" placeholder option shown at the beginning.</li>\n</ol>\n<div class=\"notecard note\">\n<p><strong>Note:</strong>\nYou can also <a href=\"https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/simple-else-if.html\" class=\"external\" target=\"_blank\">find this example on GitHub</a> (<a href=\"https://mdn.github.io/learning-area/javascript/building-blocks/simple-else-if.html\" class=\"external\" target=\"_blank\">see it running live</a> on there also.)</p>\n</div>"}},{"type":"prose","value":{"id":"a_note_on_comparison_operators","title":"A note on comparison operators","isH3":true,"content":"<p>Comparison operators are used to test the conditions inside our conditional statements. We first looked at comparison operators back in our <a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Math#comparison_operators\">Basic math in JavaScript — numbers and operators</a> article. Our choices are:</p>\n<ul>\n<li><code>===</code> and <code>!==</code> — test if one value is identical to, or not identical to, another.</li>\n<li><code><</code> and <code>></code> — test if one value is less than or greater than another.</li>\n<li><code><=</code> and <code>>=</code> — test if one value is less than or equal to, or greater than or equal to, another.</li>\n</ul>\n<p>We wanted to make a special mention of testing boolean (<code>true</code>/<code>false</code>) values, and a common pattern you'll come across again and again. Any value that is not <code>false</code>, <code>undefined</code>, <code>null</code>, <code>0</code>, <code>NaN</code>, or an empty string (<code>''</code>) actually returns <code>true</code> when tested as a conditional statement, therefore you can use a variable name on its own to test whether it is <code>true</code>, or even that it exists (that is, it is not undefined.) So 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>let cheese = \"Cheddar\";\n\nif (cheese) {\n console.log(\"Yay! Cheese available for making cheese on toast.\");\n} else {\n console.log(\"No cheese on toast for you today.\");\n}\n</code></pre></div>\n<p>And, returning to our previous example about the child doing a chore for their parent, you could write it 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>let shoppingDone = false;\nlet childsAllowance;\n\n// We don't need to explicitly specify 'shoppingDone === true'\nif (shoppingDone) {\n childsAllowance = 10;\n} else {\n childsAllowance = 5;\n}\n</code></pre></div>"}},{"type":"prose","value":{"id":"nesting_if...else","title":"Nesting if...else","isH3":true,"content":"<p>It is perfectly OK to put one <code>if...else</code> statement inside another one — to nest them. For example, we could update our weather forecast application to show a further set of choices depending on what the temperature is:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>if (choice === \"sunny\") {\n if (temperature < 86) {\n para.textContent = `It is ${temperature} degrees outside — nice and sunny. Let's go out to the beach, or the park, and get an ice cream.`;\n } else if (temperature >= 86) {\n para.textContent = `It is ${temperature} degrees outside — REALLY HOT! If you want to go outside, make sure to put some sunscreen on.`;\n }\n}\n</code></pre></div>\n<p>Even though the code all works together, each <code>if...else</code> statement works completely independently of the other one.</p>"}},{"type":"prose","value":{"id":"logical_operators_and_or_and_not","title":"Logical operators: AND, OR and NOT","isH3":true,"content":"<p>If you want to test multiple conditions without writing nested <code>if...else</code> statements, <a href=\"/en-US/docs/Web/JavaScript/Reference/Operators\">logical operators</a> can help you. When used in conditions, the first two do the following:</p>\n<ul>\n<li><code>&&</code> — AND; allows you to chain together two or more expressions so that all of them have to individually evaluate to <code>true</code> for the whole expression to return <code>true</code>.</li>\n<li><code>||</code> — OR; allows you to chain together two or more expressions so that one or more of them have to individually evaluate to <code>true</code> for the whole expression to return <code>true</code>.</li>\n</ul>\n<p>To give you an AND example, the previous example snippet can be rewritten to this:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>if (choice === \"sunny\" && temperature < 86) {\n para.textContent = `It is ${temperature} degrees outside — nice and sunny. Let's go out to the beach, or the park, and get an ice cream.`;\n} else if (choice === \"sunny\" && temperature >= 86) {\n para.textContent = `It is ${temperature} degrees outside — REALLY HOT! If you want to go outside, make sure to put some sunscreen on.`;\n}\n</code></pre></div>\n<p>So for example, the first code block will only be run if <code>choice === 'sunny'</code> <em>and</em> <code>temperature < 86</code> return <code>true</code>.</p>\n<p>Let's look at a quick OR example:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>if (iceCreamVanOutside || houseStatus === \"on fire\") {\n console.log(\"You should leave the house quickly.\");\n} else {\n console.log(\"Probably should just stay in then.\");\n}\n</code></pre></div>\n<p>The last type of logical operator, NOT, expressed by the <code>!</code> operator, can be used to negate an expression. Let's combine it with OR in the above example:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>if (!(iceCreamVanOutside || houseStatus === \"on fire\")) {\n console.log(\"Probably should just stay in then.\");\n} else {\n console.log(\"You should leave the house quickly.\");\n}\n</code></pre></div>\n<p>In this snippet, if the OR statement returns <code>true</code>, the NOT operator will negate it so that the overall expression returns <code>false</code>.</p>\n<p>You can combine as many logical statements together as you want, in whatever structure. The following example executes the code inside only if both OR statements return true, meaning that the overall AND statement will return true:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>if ((x === 5 || y > 3 || z <= 10) && (loggedIn || userName === \"Steve\")) {\n // run the code\n}\n</code></pre></div>\n<p>A common mistake when using the logical OR operator in conditional statements is to try to state the variable whose value you are checking once, and then give a list of values it could be to return true, separated by <code>||</code> (OR) operators. For example:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js example-bad notranslate\"><code>if (x === 5 || 7 || 10 || 20) {\n // run my code\n}\n</code></pre></div>\n<p>In this case, the condition inside <code>if ()</code> will always evaluate to true since 7 (or any other non-zero value) always evaluates to <code>true</code>. This condition is actually saying \"if x equals 5, or 7 is true — which it always is\". This is logically not what we want! To make this work you've got to specify a complete test on either side of each OR operator:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>if (x === 5 || x === 7 || x === 10 || x === 20) {\n // run my code\n}\n</code></pre></div>"}},{"type":"prose","value":{"id":"switch_statements","title":"switch statements","isH3":false,"content":"<p><code>if...else</code> statements do the job of enabling conditional code well, but they are not without their downsides. They are mainly good for cases where you've got a couple of choices, and each one requires a reasonable amount of code to be run, and/or the conditions are complex (for example, multiple logical operators). For cases where you just want to set a variable to a certain choice of value or print out a particular statement depending on a condition, the syntax can be a bit cumbersome, especially if you've got a large number of choices.</p>\n<p>In such a case, <a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/switch\"><code>switch</code> statements</a> are your friend — they take a single expression/value as an input, and then look through several choices until they find one that matches that value, executing the corresponding code that goes along with it. Here's some more pseudocode, to give you an idea:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>switch (expression) {\n case choice1:\n // run this code\n break;\n\n case choice2:\n // run this code instead\n break;\n\n // include as many cases as you like\n\n default:\n // actually, just run this code\n break;\n}\n</code></pre></div>\n<p>Here we've got:</p>\n<ol>\n<li>The keyword <code>switch</code>, followed by a set of parentheses.</li>\n<li>An expression or value inside the parentheses.</li>\n<li>The keyword <code>case</code>, followed by a choice that the expression/value could be, followed by a colon.</li>\n<li>Some code to run if the choice matches the expression.</li>\n<li>A <code>break</code> statement, followed by a semicolon. If the previous choice matches the expression/value, the browser stops executing the code block here, and moves on to any code that appears below the switch statement.</li>\n<li>As many other cases (bullets 3–5) as you like.</li>\n<li>The keyword <code>default</code>, followed by exactly the same code pattern as one of the cases (bullets 3–5), except that <code>default</code> does not have a choice after it, and you don't need the <code>break</code> statement as there is nothing to run after this in the block anyway. This is the default option that runs if none of the choices match.</li>\n</ol>\n<div class=\"notecard note\">\n<p><strong>Note:</strong>\nYou don't have to include the <code>default</code> section — you can safely omit it if there is no chance that the expression could end up equaling an unknown value. If there is a chance of this, however, you need to include it to handle unknown cases.</p>\n</div>"}},{"type":"prose","value":{"id":"a_switch_example","title":"A switch example","isH3":true,"content":"<p>Let's have a look at a real example — we'll rewrite our weather forecast application to use a switch statement instead:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">html</span></div><pre class=\"brush: html notranslate\"><code><label for=\"weather\">Select the weather type today: </label>\n<select id=\"weather\">\n <option value=\"\">--Make a choice--</option>\n <option value=\"sunny\">Sunny</option>\n <option value=\"rainy\">Rainy</option>\n <option value=\"snowing\">Snowing</option>\n <option value=\"overcast\">Overcast</option>\n</select>\n\n<p></p>\n</code></pre></div>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const select = document.querySelector(\"select\");\nconst para = document.querySelector(\"p\");\n\nselect.addEventListener(\"change\", setWeather);\n\nfunction setWeather() {\n const choice = select.value;\n\n switch (choice) {\n case \"sunny\":\n para.textContent =\n \"It is nice and sunny outside today. Wear shorts! Go to the beach, or the park, and get an ice cream.\";\n break;\n case \"rainy\":\n para.textContent =\n \"Rain is falling outside; take a rain coat and an umbrella, and don't stay out for too long.\";\n break;\n case \"snowing\":\n para.textContent =\n \"The snow is coming down — it is freezing! Best to stay in with a cup of hot chocolate, or go build a snowman.\";\n break;\n case \"overcast\":\n para.textContent =\n \"It isn't raining, but the sky is grey and gloomy; it could turn any minute, so take a rain coat just in case.\";\n break;\n default:\n para.textContent = \"\";\n }\n}\n</code></pre></div>\n<div class=\"code-example\"><div class=\"example-header\"></div><iframe class=\"sample-code-frame\" title=\"A switch example sample\" id=\"frame_a_switch_example\" width=\"100%\" height=\"100\" src=\"about:blank\" data-live-path=\"/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/\" data-live-id=\"a_switch_example\" sandbox=\"allow-same-origin allow-scripts\" loading=\"lazy\"></iframe></div>\n<div class=\"notecard note\">\n<p><strong>Note:</strong>\nYou can also <a href=\"https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/simple-switch.html\" class=\"external\" target=\"_blank\">find this example on GitHub</a> (see it <a href=\"https://mdn.github.io/learning-area/javascript/building-blocks/simple-switch.html\" class=\"external\" target=\"_blank\">running live</a> on there also.)</p>\n</div>"}},{"type":"prose","value":{"id":"ternary_operator","title":"Ternary operator","isH3":false,"content":"<p>There is one final bit of syntax we want to introduce you to before we get you to play with some examples. The <a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_operator\">ternary or conditional operator</a> is a small bit of syntax that tests a condition and returns one value/expression if it is <code>true</code>, and another if it is <code>false</code> — this can be useful in some situations, and can take up a lot less code than an <code>if...else</code> block if you have two choices that are chosen between via a <code>true</code>/<code>false</code> condition. The pseudocode looks 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>condition ? run this code : run this code instead\n</code></pre></div>\n<p>So let's look at an 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 greeting = isBirthday\n ? \"Happy birthday Mrs. Smith — we hope you have a great day!\"\n : \"Good morning Mrs. Smith.\";\n</code></pre></div>\n<p>Here we have a variable called <code>isBirthday</code> — if this is <code>true</code>, we give our guest a happy birthday message; if not, we give her the standard daily greeting.</p>"}},{"type":"prose","value":{"id":"ternary_operator_example","title":"Ternary operator example","isH3":true,"content":"<p>The ternary operator is not just for setting variable values; you can also run functions, or lines of code — anything you like. The following live example shows a simple theme chooser where the styling for the site is applied using a ternary operator.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">html</span></div><pre class=\"brush: html notranslate\"><code><label for=\"theme\">Select theme: </label>\n<select id=\"theme\">\n <option value=\"white\">White</option>\n <option value=\"black\">Black</option>\n</select>\n\n<h1>This is my website</h1>\n</code></pre></div>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const select = document.querySelector(\"select\");\nconst html = document.querySelector(\"html\");\ndocument.body.style.padding = \"10px\";\n\nfunction update(bgColor, textColor) {\n html.style.backgroundColor = bgColor;\n html.style.color = textColor;\n}\n\nselect.addEventListener(\"change\", () =>\n select.value === \"black\"\n ? update(\"black\", \"white\")\n : update(\"white\", \"black\"),\n);\n</code></pre></div>\n<div class=\"code-example\"><div class=\"example-header\"></div><iframe class=\"sample-code-frame\" title=\"Ternary operator example sample\" id=\"frame_ternary_operator_example\" width=\"100%\" height=\"300\" src=\"about:blank\" data-live-path=\"/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/\" data-live-id=\"ternary_operator_example\" sandbox=\"allow-same-origin allow-scripts\" loading=\"lazy\"></iframe></div>\n<p>Here we've got a <a href=\"/en-US/docs/Web/HTML/Element/select\"><code><select></code></a> element to choose a theme (black or white), plus a simple <a href=\"/en-US/docs/Web/HTML/Element/Heading_Elements\">h1</a> to display a website title. We also have a function called <code>update()</code>, which takes two colors as parameters (inputs). The website's background color is set to the first provided color, and its text color is set to the second provided color.</p>\n<p>Finally, we've also got an <a href=\"/en-US/docs/Web/API/HTMLElement/change_event\">onchange</a> event listener that serves to run a function containing a ternary operator. It starts with a test condition — <code>select.value === 'black'</code>. If this returns <code>true</code>, we run the <code>update()</code> function with parameters of black and white, meaning that we end up with a background color of black and a text color of white. If it returns <code>false</code>, we run the <code>update()</code> function with parameters of white and black, meaning that the site colors are inverted.</p>\n<div class=\"notecard note\">\n<p><strong>Note:</strong>\nYou can also <a href=\"https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/simple-ternary.html\" class=\"external\" target=\"_blank\">find this example on GitHub</a> (see it <a href=\"https://mdn.github.io/learning-area/javascript/building-blocks/simple-ternary.html\" class=\"external\" target=\"_blank\">running live</a> on there also.)</p>\n</div>"}},{"type":"prose","value":{"id":"active_learning_a_simple_calendar","title":"Active learning: A simple calendar","isH3":false,"content":"<p>In this example, you are going to help us finish a simple calendar application. In the code you've got:</p>\n<ul>\n<li>A <a href=\"/en-US/docs/Web/HTML/Element/select\"><code><select></code></a> element to allow the user to choose between different months.</li>\n<li>An <code>onchange</code> event handler to detect when the value selected in the <code><select></code> menu is changed.</li>\n<li>A function called <code>createCalendar()</code> that draws the calendar and displays the correct month in the <a href=\"/en-US/docs/Web/HTML/Element/Heading_Elements\">h1</a> element.</li>\n</ul>\n<p>We need you to write a conditional statement inside the <code>createCalendar()</code> function, just below the <code>// ADD CONDITIONAL HERE</code> comment. It should:</p>\n<ol>\n<li>Look at the selected month (stored in the <code>choice</code> variable. This will be the <code><select></code> element value after the value changes, so \"January\" for example.)</li>\n<li>Assign the <code>days</code> variable to be equal to the number of days in the selected month. To do this you'll have to look up the number of days in each month of the year. You can ignore leap years for the purposes of this example.</li>\n</ol>\n<p>Hints:</p>\n<ul>\n<li>You are advised to use logical OR to group multiple months together into a single condition; many of them share the same number of days.</li>\n<li>Think about which number of days is the most common, and use that as a default value.</li>\n</ul>\n<p>If you make a mistake, you can always reset the example with the \"Reset\" button. If you get really stuck, press \"Show solution\" to see a solution.</p>\n<div class=\"code-example\"><pre class=\"brush: html hidden notranslate\"><code><h2>Live output</h2>\n<iframe id=\"output\" width=\"100%\" height=\"600px\"></iframe>\n\n<h2>Editable code</h2>\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: 400px;width: 95%\">\nconst select = document.querySelector(\"select\");\nconst list = document.querySelector(\"ul\");\nconst h1 = document.querySelector(\"h1\");\n\nselect.addEventListener(\"change\", () => {\n const choice = select.value;\n createCalendar(choice);\n});\n\nfunction createCalendar(month) {\n let days = 31;\n\n // ADD CONDITIONAL HERE\n\n list.textContent = \"\";\n h1.textContent = month;\n for (let i = 1; i <= days; i++) {\n const listItem = document.createElement(\"li\");\n listItem.textContent = i;\n list.appendChild(listItem);\n }\n}\n\nselect.value = \"January\";\ncreateCalendar(\"January\");\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 reset = document.getElementById(\"reset\");\nconst solution = document.getElementById(\"solution\");\nconst outputIFrame = document.querySelector(\"#output\");\nconst textarea = document.getElementById(\"code\");\nconst initialCode = textarea.value;\nlet userCode = textarea.value;\n\nconst solutionCode = `const select = document.querySelector(\"select\");\nconst list = document.querySelector(\"ul\");\nconst h1 = document.querySelector(\"h1\");\n\nselect.addEventListener(\"change\", () => {\n const choice = select.value;\n createCalendar(choice);\n});\n\nfunction createCalendar(month) {\n let days = 31;\n\n if (month === \"February\") {\n days = 28;\n } else if (\n month === \"April\" ||\n month === \"June\" ||\n month === \"September\" ||\n month === \"November\"\n ) {\n days = 30;\n }\n\n list.textContent = \"\";\n h1.textContent = month;\n for (let i = 1; i <= days; i++) {\n const listItem = document.createElement(\"li\");\n listItem.textContent = i;\n list.appendChild(listItem);\n }\n}\n\nselect.value = \"January\";\ncreateCalendar(\"January\");`;\n\nfunction outputDocument(code) {\n const outputBody = `\n<div class=\"output\" style=\"height: 500px; overflow: auto\">\n <label for=\"month\">Select month: </label>\n <select id=\"month\">\n <option value=\"January\">January</option>\n <option value=\"February\">February</option>\n <option value=\"March\">March</option>\n <option value=\"April\">April</option>\n <option value=\"May\">May</option>\n <option value=\"June\">June</option>\n <option value=\"July\">July</option>\n <option value=\"August\">August</option>\n <option value=\"September\">September</option>\n <option value=\"October\">October</option>\n <option value=\"November\">November</option>\n <option value=\"December\">December</option>\n </select>\n\n <h1></h1>\n\n <ul></ul>\n</div>`;\n\n const outputStyle = `\n.output * {\n box-sizing: border-box;\n}\n\n.output ul {\n padding-left: 0;\n}\n\n.output li {\n display: block;\n float: left;\n width: 25%;\n border: 2px solid white;\n padding: 5px;\n height: 40px;\n background-color: #4a2db6;\n color: white;\n}\nhtml {\n font-family: sans-serif;\n}\n\nh2 {\n font-size: 16px;\n}`;\n return `\n<!doctype html>\n<html>\n <head>\n <style>${outputStyle}</style>\n </head>\n <body>\n ${outputBody}\n <script>${code}<${\"/\"}script>\n </body>\n</html>`;\n}\n\nfunction update() {\n output.setAttribute(\"srcdoc\", outputDocument(textarea.value));\n}\n\nupdate();\n\ntextarea.addEventListener(\"input\", update);\n\nreset.addEventListener(\"click\", () => {\n textarea.value = initialCode;\n userEntry = textarea.value;\n solution.value = \"Show solution\";\n update();\n});\n\nsolution.addEventListener(\"click\", () => {\n if (solution.value === \"Show solution\") {\n // remember the state of the user's code\n // so we can restore it\n userCode = textarea.value;\n textarea.value = solutionCode;\n solution.value = \"Hide solution\";\n } else {\n textarea.value = userCode;\n solution.value = \"Show solution\";\n }\n update();\n});\n\n// stop tab key tabbing out of textarea and\n// make it write a tab at the caret position instead\ntextarea.onkeydown = (e) => {\n if (e.code === \"Tab\") {\n e.preventDefault();\n insertAtCaret(\"\\t\");\n }\n\n if (e.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</code></pre></div>\n<div class=\"code-example\"><div class=\"example-header\"></div><iframe class=\"sample-code-frame\" title=\"Active learning A simple calendar sample\" id=\"frame_active_learning_a_simple_calendar\" width=\"100%\" height=\"1210\" src=\"about:blank\" data-live-path=\"/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/\" data-live-id=\"active_learning_a_simple_calendar\" sandbox=\"allow-same-origin allow-scripts\" loading=\"lazy\"></iframe></div>"}},{"type":"prose","value":{"id":"active_learning_more_color_choices","title":"Active learning: More color choices","isH3":false,"content":"<p>In this example, you are going to take the ternary operator example we saw earlier and convert the ternary operator into a switch statement to allow us to apply more choices to the simple website. Look at the <a href=\"/en-US/docs/Web/HTML/Element/select\"><code><select></code></a> — this time you'll see that it has not two theme options, but five. You need to add a switch statement just underneath the <code>// ADD SWITCH STATEMENT</code> comment:</p>\n<ul>\n<li>It should accept the <code>choice</code> variable as its input expression.</li>\n<li>For each case, the choice should equal one of the possible <code><option></code> values that can be selected, that is, <code>white</code>, <code>black</code>, <code>purple</code>, <code>yellow</code>, or <code>psychedelic</code>. Note that the option values are lowercase, while the option <em>labels</em>, as displayed in the live output, are capitalized. You should use the lowercase values in your code.</li>\n<li>For each case, the <code>update()</code> function should be run, and be passed two color values, the first one for the background color, and the second one for the text color. Remember that color values are strings, so they need to be wrapped in quotes.</li>\n</ul>\n<p>If you make a mistake, you can always reset the example with the \"Reset\" button. If you get really stuck, press \"Show solution\" to see a solution.</p>\n<div class=\"code-example\"><pre class=\"brush: html hidden notranslate\"><code><h2>Live output</h2>\n<iframe id=\"output\" width=\"100%\" height=\"350px\"></iframe>\n\n<h2>Editable code</h2>\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: 400px;width: 95%\">\nconst select = document.querySelector('select');\nconst html = document.querySelector('.output');\n\nselect.addEventListener('change', () => {\n const choice = select.value;\n\n // ADD SWITCH STATEMENT\n});\n\nfunction update(bgColor, textColor) {\n html.style.backgroundColor = bgColor;\n html.style.color = textColor;\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 reset = document.getElementById(\"reset\");\nconst solution = document.getElementById(\"solution\");\nconst outputIFrame = document.querySelector(\"#output\");\nconst textarea = document.getElementById(\"code\");\nconst initialCode = textarea.value;\nlet userCode = textarea.value;\n\nconst solutionCode = `const select = document.querySelector('select');\nconst html = document.querySelector('.output');\n\nselect.addEventListener('change', () => {\n const choice = select.value;\n\n switch(choice) {\n case 'black':\n update('black','white');\n break;\n case 'white':\n update('white','black');\n break;\n case 'purple':\n update('purple','white');\n break;\n case 'yellow':\n update('yellow','purple');\n break;\n case 'psychedelic':\n update('lime','purple');\n break;\n }\n});\n\nfunction update(bgColor, textColor) {\n html.style.backgroundColor = bgColor;\n html.style.color = textColor;\n}`;\n\nfunction outputDocument(code) {\n const outputBody = `\n<div class=\"output\" style=\"height: 300px;\">\n <label for=\"theme\">Select theme: </label>\n <select id=\"theme\">\n <option value=\"white\">White</option>\n <option value=\"black\">Black</option>\n <option value=\"purple\">Purple</option>\n <option value=\"yellow\">Yellow</option>\n <option value=\"psychedelic\">Psychedelic</option>\n </select>\n\n <h1>This is my website</h1>\n</div>`;\n\n return `\n<!doctype html>\n<html>\n <head>\n </head>\n <body>\n ${outputBody}\n <script>${code}<${\"/\"}script>\n </body>\n</html>`;\n}\n\nfunction update() {\n output.setAttribute(\"srcdoc\", outputDocument(textarea.value));\n}\n\nupdate();\n\ntextarea.addEventListener(\"input\", update);\n\nreset.addEventListener(\"click\", () => {\n textarea.value = initialCode;\n userEntry = textarea.value;\n solution.value = \"Show solution\";\n update();\n});\n\nsolution.addEventListener(\"click\", () => {\n if (solution.value === \"Show solution\") {\n // remember the state of the user's code\n // so we can restore it\n userCode = textarea.value;\n textarea.value = solutionCode;\n solution.value = \"Hide solution\";\n } else {\n textarea.value = userCode;\n solution.value = \"Show solution\";\n }\n update();\n});\n\n// stop tab key tabbing out of textarea and\n// make it write a tab at the caret position instead\ntextarea.onkeydown = (e) => {\n if (e.code === \"Tab\") {\n e.preventDefault();\n insertAtCaret(\"\\t\");\n }\n\n if (e.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</code></pre></div>\n<div class=\"code-example\"><div class=\"example-header\"></div><iframe class=\"sample-code-frame\" title=\"Active learning More color choices sample\" id=\"frame_active_learning_more_color_choices\" width=\"100%\" height=\"950\" src=\"about:blank\" data-live-path=\"/en-US/docs/Learn_web_development/Core/Scripting/Conditionals/\" data-live-id=\"active_learning_more_color_choices\" 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_web_development/Core/Scripting/Test_your_skills:_Conditionals\">Test your skills: Conditionals</a>.</p>"}},{"type":"prose","value":{"id":"summary","title":"Summary","isH3":false,"content":"<p>That's all you really need to know about conditional structures in JavaScript right now! Next up, we'll look at looping through code.</p>"}},{"type":"prose","value":{"id":"see_also","title":"See also","isH3":false,"content":"<ul>\n<li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Math#comparison_operators\">Comparison operators</a></li>\n<li><a href=\"/en-US/docs/Web/JavaScript/Guide/Control_flow_and_error_handling#conditional_statements\">Conditional statements in detail</a></li>\n<li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/if...else\">if...else reference</a></li>\n<li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_operator\">Conditional (ternary) operator reference</a></li>\n</ul>\n<ul class=\"prev-next\"><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Core/Scripting/Silly_story_generator\"><span class=\"button-wrap\"> Previous </span></a></li><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Core/Scripting\"><span class=\"button-wrap\"> Overview: Dynamic scripting with JavaScript</span></a></li><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Core/Scripting/Loops\"><span class=\"button-wrap\"> Next </span></a></li></ul>"}}],"isActive":true,"isMarkdown":true,"isTranslated":false,"locale":"en-US","mdn_url":"/en-US/docs/Learn_web_development/Core/Scripting/Conditionals","modified":"2024-12-19T15:37:45.000Z","native":"English (US)","noIndexing":false,"other_translations":[{"locale":"de","title":"Entscheidungen in Ihrem Code treffen — Konditionalen","native":"Deutsch"},{"locale":"es","title":"Tomando decisiones en tu código — condicionales","native":"Español"},{"locale":"fr","title":"Prendre des décisions dans le code — conditions","native":"Français"},{"locale":"ja","title":"コードでの意思決定 — 条件文","native":"日本語"},{"locale":"ko","title":"판단 내리기 — 조건문","native":"한국어"},{"locale":"pt-BR","title":"Tomando decisões no seu código — condicionais","native":"Português (do Brasil)"},{"locale":"ru","title":"Принятие решений в вашем коде — условные конструкции","native":"Русский"},{"locale":"zh-CN","title":"在代码中做决定——条件语句","native":"中文 (简体)"},{"locale":"zh-TW","title":"在代碼中做出決定 - 條件","native":"正體中文 (繁體)"}],"pageTitle":"Making decisions in your code — conditionals - Learn web development | MDN","parents":[{"uri":"/en-US/docs/Learn_web_development","title":"Learn"},{"uri":"/en-US/docs/Learn_web_development/Core","title":"Core learning modules"},{"uri":"/en-US/docs/Learn_web_development/Core/Scripting","title":"Dynamic scripting with JavaScript"},{"uri":"/en-US/docs/Learn_web_development/Core/Scripting/Conditionals","title":"Making decisions in your code — conditionals"}],"popularity":null,"short_title":"Making decisions in your code — conditionals","sidebarHTML":"<ol><li class=\"section\"><a href=\"/en-US/docs/Learn_web_development/Getting_started\">Getting started modules</a></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup\">Environment setup</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup/Installing_software\">Installing basic software</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup/Browsing_the_web\">Browsing the web</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup/Code_editors\">Code editors</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup/Dealing_with_files\">Dealing with files</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup/Command_line\">Command line crash course</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website\">Your first website</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website/What_will_your_website_look_like\">What will your website look like?</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Creating_the_content\">HTML: Creating the content</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Styling_the_content\">CSS: Styling the content</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Adding_interactivity\">JavaScript: Adding interactivity</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Publishing_your_website\">Publishing your website</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Getting_started/Web_standards\">Web standards</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Web_standards/How_the_web_works\">How the web works</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Web_standards/The_web_standards_model\">The web standards model</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Web_standards/How_browsers_load_websites\">How browsers load websites</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills\">Soft skills</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Research_and_learning\">Research and learning</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Collaboration_and_teamwork\">Collaboration and teamwork</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Workflows_and_processes\">Workflows and processes</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Job_interviews\">Succeeding in job interviews</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn_web_development/Core\">Core modules</a></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content\">Structuring content with HTML</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Basic_HTML_syntax\">Basic HTML syntax</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Webpage_metadata\">What's in the head? Webpage metadata</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Headings_and_paragraphs\">Headings and paragraphs in HTML</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Emphasis_and_importance\">Emphasis and importance</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Lists\">Lists</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Structuring_documents\">Structuring documents</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Advanced_text_features\">Advanced text features</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Creating_links\">Creating links</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Marking_up_a_letter\">Challenge: Marking up a letter</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Structuring_a_page_of_content\">Challenge: Structuring a page of content</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_images\">HTML images</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_video_and_audio\">HTML video and audio</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Mozilla_splash_page\">Challenge: Mozilla splash page</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_table_basics\">HTML table basics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Table_accessibility\">HTML table accessibility</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Planet_data_table\">Challenge: Structuring a planet data table</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_forms\">Forms and buttons in HTML</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Debugging_HTML\">Debugging HTML</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics\">CSS styling basics</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/What_is_CSS\">What is CSS?</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Getting_started\">Getting started with CSS</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Styling_a_bio_page\">Challenge: Styling a biography page</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Basic_selectors\">Basic CSS selectors</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Attribute_selectors\">Attribute selectors</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Pseudo_classes_and_elements\">Pseudo-classes and pseudo-elements</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Combinators\">Combinators</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Box_model\">The box model</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Handling_conflicts\">Handling conflicts</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Values_and_units\">CSS values and units</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Sizing\">Sizing items in CSS</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Backgrounds_and_borders\">Backgrounds and borders</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Overflow\">Overflowing content</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Images_media_forms\">Images, media, and form elements</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Tables\">Styling tables</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Debugging_CSS\">Debugging CSS</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Fundamental_CSS_comprehension\">Challenge: Fundamental CSS comprehension</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Fancy_letterheaded_paper\">Challenge: Creating fancy letterheaded paper</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Cool-looking_box\">Challenge: A cool-looking box</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling\">CSS text styling</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling/Fundamentals\">Fundamental text and font styling</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling/Styling_lists\">Styling lists</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling/Styling_links\">Styling links</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling/Web_fonts\">Web fonts</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling/Typesetting_a_homepage\">Challenge: Typesetting a community school homepage</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout\">CSS layout</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Introduction\">Introduction to CSS layout</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Floats\">Floats</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Positioning\">Positioning</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Flexbox\">Flexbox</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Grids\">CSS grid layout</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Responsive_Design\">Responsive design</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Media_queries\">Media query fundamentals</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Fundamental_Layout_Comprehension\">Challenge: Fundamental layout comprehension</a></li></ol></details></li><li class=\"toggle\"><details open=\"\"><summary><a href=\"/en-US/docs/Learn_web_development/Core/Scripting\">Dynamic scripting with JavaScript</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/What_is_JavaScript\">What is JavaScript?</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/A_first_splash\">A first splash into JavaScript</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/What_went_wrong\">What went wrong? Troubleshooting JavaScript</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Variables\">Storing the information you need — Variables</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Math\">Basic math in JavaScript — numbers and operators</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Strings\">Handling text — strings in JavaScript</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Useful_string_methods\">Useful string methods</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Arrays\">Arrays</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Silly_story_generator\">Challenge: Silly story generator</a></li><li><em><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Conditionals\" aria-current=\"page\">Making decisions in your code — conditionals</a></em></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Loops\">Looping code</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Functions\">Functions — reusable blocks of code</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Build_your_own_function\">Build your own function</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Return_values\">Function return values</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Events\">Introduction to events</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Event_bubbling\">Event bubbling</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Image_gallery\">Challenge: Image gallery</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Object_basics\">JavaScript object basics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/DOM_scripting\">DOM scripting introduction</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Network_requests\">Making network requests with JavaScript</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/JSON\">Working with JSON</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Debugging_JavaScript\">Debugging JavaScript and handling errors</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries\">JavaScript frameworks and libraries</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/Introduction\">Introduction to client-side frameworks</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/Main_features\">Framework main features</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_getting_started\">Getting started with React</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_todo_list_beginning\">Beginning our React todo list</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_components\">Componentizing our React app</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_events_state\">React interactivity: Events and state</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_filtering_conditional_rendering\">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_accessibility\">Accessibility in React</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_resources\">React resources</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility\">Accessibility</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/What_is_accessibility\">What is accessibility?</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/Tooling\">Accessibility tooling and assistive technology</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/HTML\">HTML: A good basis for accessibility</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/CSS_and_JavaScript\">CSS and JavaScript accessibility best practices</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/WAI-ARIA_basics\">WAI-ARIA basics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/Multimedia\">Accessible multimedia</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/Mobile\">Mobile accessibility</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/Accessibility_troubleshooting\">Challenge: Accessibility troubleshooting</a></li></ol></details></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Design_for_developers\">Design for developers</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Version_control\">Version control</a></li><li class=\"section\"><a href=\"/en-US/docs/Learn_web_development/Extensions\">Extension modules</a></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects\">Advanced JavaScript objects</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_prototypes\">Object prototypes</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object-oriented_programming\">Object-oriented programming</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Classes_in_JavaScript\">Classes in JavaScript</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_building_practice\">Object building practice</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Adding_bouncing_balls_features\">Challenge: Adding features to our bouncing balls demo</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs\">Client-side web APIs</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Introduction\">Introduction to web APIs</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Video_and_audio_APIs\">Video and Audio APIs</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Drawing_graphics\">Drawing graphics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Client-side_storage\">Client-side storage</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Third_party_APIs\">Third-party APIs</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS\">Asynchronous JavaScript</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS/Introducing\">Introducing asynchronous JavaScript</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS/Promises\">How to use promises</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS/Implementing_a_promise-based_API\">How to implement a promise-based API</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS/Introducing_workers\">Introducing workers</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS/Sequencing_animations\">Challenge: Sequencing animations</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms\">Web forms</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Your_first_form\">Your first form</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/How_to_structure_a_web_form\">How to structure a web form</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Basic_native_form_controls\">Basic native form controls</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/HTML5_input_types\">The HTML5 input types</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Other_form_controls\">Other form controls</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Styling_web_forms\">Styling web forms</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Advanced_form_styling\">Advanced form styling</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/UI_pseudo-classes\">UI pseudo-classes</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Form_validation\">Client-side form validation</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Sending_and_retrieving_form_data\">Sending form data</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_tools\">Understanding client-side tools</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Overview\">Client-side tooling overview</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Package_management\">Package management basics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Introducing_complete_toolchain\">Introducing a complete toolchain</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Deployment\">Deploying our app</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side\">Server-side websites</a></summary><ol><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps\">Server-side first steps</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Introduction\">Introduction to the server side</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Client-Server_overview\">Client-Server Overview</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Web_frameworks\">Server-side web frameworks</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Website_security\">Website security</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django\">Django web framework (Python)</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Introduction\">Django introduction</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/development_environment\">Setting up a Django development environment</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Tutorial_local_library_website\">Django Tutorial: The Local Library website</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/skeleton_website\">Django Tutorial Part 2: Creating a skeleton website</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Models\">Django Tutorial Part 3: Using models</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Admin_site\">Django Tutorial Part 4: Django admin site</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Home_page\">Django Tutorial Part 5: Creating our home page</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Generic_views\">Django Tutorial Part 6: Generic list and detail views</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Sessions\">Django Tutorial Part 7: Sessions framework</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Authentication\">Django Tutorial Part 8: User authentication and permissions</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Forms\">Django Tutorial Part 9: Working with forms</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Testing\">Django Tutorial Part 10: Testing a Django web application</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Deployment\">Django Tutorial Part 11: Deploying Django to production</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/web_application_security\">Django web application security</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/django_assessment_blog\">Assessment: DIY Django mini blog</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs\">Express web framework (Node.js)</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Introduction\">Express/Node introduction</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/development_environment\">Setting up a Node development environment</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Tutorial_local_library_website\">Express Tutorial: The Local Library website</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/skeleton_website\">Express Tutorial Part 2: Creating a skeleton website</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/mongoose\">Express Tutorial Part 3: Using a Database (with Mongoose)</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/routes\">Express Tutorial Part 4: Routes and controllers</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Displaying_data\">Express Tutorial Part 5: Displaying library data</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/forms\">Express Tutorial Part 6: Working with forms</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/deployment\">Express Tutorial Part 7: Deploying to production</a></li></ol></details></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance\">Web performance</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/why_web_performance\">The \"why\" of web performance</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/What_is_web_performance\">What is web performance?</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/Perceived_performance\">Perceived performance</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/Measuring_performance\">Measuring performance</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/Multimedia\">Multimedia: Images</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/video\">Multimedia: video</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/JavaScript\">JavaScript performance optimization</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/HTML\">HTML performance optimization</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/CSS\">CSS performance optimization</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/business_case_for_performance\">The business case for web performance</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing\">Testing</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/Introduction\">Introduction to cross-browser testing</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/Testing_strategies\">Strategies for carrying out testing</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/HTML_and_CSS\">Handling common HTML and CSS problems</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/Feature_detection\">Implementing feature detection</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/Automated_testing\">Introduction to automated testing</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/Your_own_automation_environment\">Setting up your own test automation environment</a></li></ol></details></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Transform_animate\">Transform and animate CSS</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Security_privacy\">Security and privacy</a></li><li class=\"section\">Further resources</li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Howto\">How to solve common problems</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Howto/Solve_HTML_problems\">Solve common HTML problems</a></li><li><a href=\"/en-US/docs/Learn_web_development/Howto/Solve_CSS_problems\">Solve common CSS problems</a></li><li><a href=\"/en-US/docs/Learn_web_development/Howto/Solve_JavaScript_problems\">Solve common JavaScript problems</a></li><li><a href=\"/en-US/docs/Learn_web_development/Howto/Web_mechanics\">Web mechanics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Howto/Tools_and_setup\">Tools and setup</a></li><li><a href=\"/en-US/docs/Learn_web_development/Howto/Design_and_accessibility\">Design and accessibility</a></li></ol></details></li><li><a href=\"/en-US/docs/Learn_web_development/About\">About</a></li><li><a href=\"/en-US/docs/Learn_web_development/Educators\">Resources for educators</a></li><li><a href=\"/en-US/docs/Learn_web_development/Changelog\">Changelog</a></li></ol>","source":{"folder":"en-us/learn_web_development/core/scripting/conditionals","github_url":"https://github.com/mdn/content/blob/main/files/en-us/learn_web_development/core/scripting/conditionals/index.md","last_commit_url":"https://github.com/mdn/content/commit/5b20f5f4265f988f80f513db0e4b35c7e0cd70dc","filename":"index.md"},"summary":"In any programming language, the code needs to make decisions and carry out actions accordingly depending on different inputs. For example, in a game, if the player's number of lives is 0, then it's game over. In a weather app, if it is being looked at in the morning, show a sunrise graphic; show stars and a moon if it is nighttime. In this article, we'll explore how so-called conditional statements work in JavaScript.","title":"Making decisions in your code — conditionals","toc":[{"text":"You can have it on one condition!","id":"you_can_have_it_on_one_condition!"},{"text":"if...else statements","id":"if...else_statements"},{"text":"switch statements","id":"switch_statements"},{"text":"Ternary operator","id":"ternary_operator"},{"text":"Active learning: A simple calendar","id":"active_learning_a_simple_calendar"},{"text":"Active learning: More color choices","id":"active_learning_more_color_choices"},{"text":"Test your skills!","id":"test_your_skills!"},{"text":"Summary","id":"summary"},{"text":"See also","id":"see_also"}],"pageType":"learn-module-chapter"}}</script></body></html>