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href="/zh-CN/docs/Learn_web_development/Core/Frameworks_libraries/React_getting_started">React 入门</a></li><li><a href="/zh-CN/docs/Learn_web_development/Core/Frameworks_libraries/React_todo_list_beginning">开始我们的 React 待办清单</a></li><li><a href="/zh-CN/docs/Learn_web_development/Core/Frameworks_libraries/React_components">组件化我们的 React App</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_events_state" class="only-in-en-us">React interactivity: Events and state</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_filtering_conditional_rendering" class="only-in-en-us">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_accessibility" class="only-in-en-us">Accessibility in React</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_resources" class="only-in-en-us">React resources</a></li></ol></details></li><li class="toggle"><details><summary><a href="/zh-CN/docs/Learn_web_development/Core/Accessibility">无障碍</a></summary><ol><li><a href="/zh-CN/docs/Learn_web_development/Core/Accessibility/What_is_accessibility">什么是无障碍？</a></li><li><a href="/zh-CN/docs/Learn_web_development/Core/Accessibility/Tooling">解决常见的无障碍问题</a></li><li><a href="/zh-CN/docs/Learn_web_development/Core/Accessibility/HTML">HTML：无障碍的良好基础</a></li><li><a href="/zh-CN/docs/Learn_web_development/Core/Accessibility/CSS_and_JavaScript">CSS 和 JavaScript 无障碍最佳实践</a></li><li><a href="/zh-CN/docs/Learn_web_development/Core/Accessibility/WAI-ARIA_basics">WAI-ARIA 基础</a></li><li><a href="/zh-CN/docs/Learn_web_development/Core/Accessibility/Multimedia">多媒体无障碍</a></li><li><a href="/zh-CN/docs/Learn_web_development/Core/Accessibility/Mobile">移动端无障碍</a></li><li><a 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href="/zh-CN/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_building_practice">实践对象构造</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Adding_bouncing_balls_features">为“弹球”示例添加新功能</a></li></ol></details></li><li class="toggle"><details><summary><a href="/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs">客户端 Web API</a></summary><ol><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs/Introduction">Web API 简介</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs/Video_and_audio_APIs">视频和音频 API</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs/Drawing_graphics">绘图</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs/Client-side_storage">客户端存储</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs/Third_party_APIs">第三方 API</a></li></ol></details></li><li 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href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/skeleton_website">Django Tutorial Part 2: 创建网站的地基</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Models">Django Tutorial Part 3: 使用模型</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Admin_site">Django Tutorial Part 4: Django 管理员站点</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Home_page">Django 教程 5：主页构建</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Generic_views">Django 教程 6: 通用列表和详细信息视图</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Sessions">Django 教程 7: 会话框架</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Authentication">Django 教程 8：用户授权与许可</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Forms">Django 教程 9: 使用表单</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Testing">Django 教程 10: 测试 Django 网页应用</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Deployment">Django 教程 11：部署 Django 到生产环境</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/web_application_security">Django Web 应用安全</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/django_assessment_blog">评估：DIY Django 微博客</a></li></ol></details></li><li class="toggle"><details><summary><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs">Express web 框架（Node.js）</a></summary><ol><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Introduction">Express/Node 入门</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/development_environment">设置 Node 开发环境</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Tutorial_local_library_website">Express 教程：本地图书馆网站</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/skeleton_website">Express 教程 2：创建站点框架</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/mongoose">Express 教程 3：使用数据库 (Mongoose)</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/routes">Express 教程 4：路由和控制器</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Displaying_data">Express 教程 5: 呈现图书馆数据</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/forms">Express 教程 6: 使用表单</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/deployment">Express 教程 7：部署到生产环境</a></li></ol></details></li></ol></details></li><li class="toggle"><details><summary><a href="/zh-CN/docs/Learn_web_development/Extensions/Performance">Web 性能</a></summary><ol><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Performance/why_web_performance">Web 性能的重要性</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Performance/What_is_web_performance">什么是 web 性能？</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Performance/Perceived_performance">感知性能</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Performance/Measuring_performance">测量性能</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Performance/Multimedia">多媒体：图片</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Performance/video">多媒体：视频</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Performance/JavaScript">JavaScript 性能优化</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Performance/HTML">HTML 性能优化</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Performance/CSS">CSS 性能优化</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Performance/business_case_for_performance">web 性能的商业案例</a></li></ol></details></li><li class="toggle"><details><summary><a href="/zh-CN/docs/Learn_web_development/Extensions/Testing">测试</a></summary><ol><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Testing/Introduction">跨浏览器测试介绍</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Testing/Testing_strategies">测试的策略</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Testing/HTML_and_CSS">处理常见的 HTML 和 CSS 问题</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Testing/Feature_detection">实现特性检测</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Testing/Automated_testing">自动化测试简介</a></li><li><a href="/zh-CN/docs/Learn_web_development/Extensions/Testing/Your_own_automation_environment">搭建自己的自动化测试环境</a></li></ol></details></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Transform_animate" class="only-in-en-us">CSS 变换与动画化</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Security_privacy" class="only-in-en-us">安全与隐私</a></li><li class="section">更多资源</li><li class="toggle"><details><summary><a href="/zh-CN/docs/Learn_web_development/Howto">如何解决常见问题</a></summary><ol><li><a href="/zh-CN/docs/Learn_web_development/Howto/Solve_HTML_problems">使用 HTML 解决常见问题</a></li><li><a href="/zh-CN/docs/Learn_web_development/Howto/Solve_CSS_problems">解决常见的 CSS 问题</a></li><li><a href="/zh-CN/docs/Learn_web_development/Howto/Solve_JavaScript_problems">解决 JavaSctript 代码的常见问题</a></li><li><a href="/zh-CN/docs/Learn_web_development/Howto/Web_mechanics">Web 机制</a></li><li><a href="/zh-CN/docs/Learn_web_development/Howto/Tools_and_setup">工具和安装</a></li><li><a href="/zh-CN/docs/Learn_web_development/Howto/Design_and_accessibility">设计与无障碍</a></li></ol></details></li><li><a href="/en-US/docs/Learn_web_development/About" class="only-in-en-us">关于</a></li><li><a href="/en-US/docs/Learn_web_development/Educators" class="only-in-en-us">面向教育工作者的资源</a></li><li><a href="/en-US/docs/Learn_web_development/Changelog" class="only-in-en-us">更新日志</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">在本文中</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#我能在哪找到函数？">我能在哪找到函数？</a></li><li class="document-toc-item "><a class="document-toc-link" href="#浏览器内置函数">浏览器内置函数</a></li><li class="document-toc-item "><a class="document-toc-link" href="#函数与方法">函数与方法</a></li><li class="document-toc-item "><a class="document-toc-link" href="#调用函数">调用函数</a></li><li class="document-toc-item "><a class="document-toc-link" href="#函数参数">函数参数</a></li><li class="document-toc-item "><a class="document-toc-link" href="#匿名函数和箭头函数">匿名函数和箭头函数</a></li><li class="document-toc-item "><a class="document-toc-link" href="#函数作用域和冲突">函数作用域和冲突</a></li><li class="document-toc-item "><a class="document-toc-link" href="#技能测试！">技能测试！</a></li><li class="document-toc-item "><a class="document-toc-link" href="#总结">总结</a></li><li class="document-toc-item "><a class="document-toc-link" href="#参见">参见</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="zh-CN"><header><h1>函数——可复用的代码块</h1></header><div class="section-content"><ul class="prev-next"><li><a class="button secondary" href="/zh-CN/docs/Learn_web_development/Core/Scripting/Loops"><span class="button-wrap"> 上一页 </span></a></li><li><a class="button secondary" href="/zh-CN/docs/Learn_web_development/Core/Scripting"><span class="button-wrap"> 概述：创建 JavaScript 代码块</span></a></li><li><a class="button secondary" href="/zh-CN/docs/Learn_web_development/Core/Scripting/Build_your_own_function"><span class="button-wrap"> 下一页 </span></a></li></ul> <p>在 JavaScript 中另一个基本概念是<strong>函数</strong>, 它允许你在一个代码块中存储一段用于处理单任务的代码，然后在任何你需要的时候用一个简短的命令来调用，而不是把相同的代码写很多次。在本文中，我们将探索函数的基本概念，如函数的基本语法、如何定义和调用函数、函数的作用域和参数。</p> <figure class="table-container"><table> <tbody> <tr> <th scope="row">前提：</th> <td> 基本的电脑知识，对 HTML 与 CSS 有基本的了解，及已阅读：<a href="/zh-CN/docs/Learn_web_development/Core/Scripting">JavaScript 第一步</a>。 </td> </tr> <tr> <th scope="row">目标：</th> <td>了解 Javascript 函数背后的基本概念。</td> </tr> </tbody> </table></figure></div><section aria-labelledby="我能在哪找到函数？"><h2 id="我能在哪找到函数？"><a href="#我能在哪找到函数？">我能在哪找到函数？</a></h2><div class="section-content"><p>在 JavaScript 中，你将发现函数无处不在。事实上，到目前为止，我们一直在使用函数；我们只是还没正式地讨论它们。然而现在是时候了，让我们开始聊聊函数，并探索它们的语法。</p> <p>几乎任何时候，只要你使用一个带有一对圆括号（<code>()</code>）的 JavaScript 结构，并且你<strong>没有</strong>使用比如 <a href="/zh-CN/docs/Learn_web_development/Core/Scripting/Loops#循环的标准">for 循环</a>、<a href="/zh-CN/docs/Learn_web_development/Core/Scripting/Loops#while_语句和_do_..._while_语句">while 或 do...while 循环</a>，或者 <a href="/zh-CN/docs/Learn_web_development/Core/Scripting/Conditionals#if...else_语句">if...else 语句</a>这样的常见的内置语言结构时，那么你就正在使用函数。</p></div></section><section aria-labelledby="浏览器内置函数"><h2 id="浏览器内置函数"><a href="#浏览器内置函数">浏览器内置函数</a></h2><div class="section-content"><p>在这套课程中我们已经使用了很多浏览器内置函数。</p> <p>例如，当我们操作一个字符串的时候：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const myText = "我是一个字符串"; const newString = myText.replace("字符串", "香肠"); console.log(newString); // replace() 字符串函数接受源字符串和目标字符串， // 将源字符串替换为目标字符串，并返回新形成的字符串 </code></pre></div> <p>或者当我们操作一个数组的时候：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const myArray = ["我", "爱", "巧克力", "青蛙"]; const madeAString = myArray.join(" "); console.log(madeAString); // join() 函数接受一个数组， // 将所有数组元素连接成一个单一的字符串，并返回这个新字符串 </code></pre></div> <p>或者当我们生成一个随机数时：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const myNumber = Math.random(); // random() 函数生成一个随机 // 数字在 0 和 1 之间，并返回该数字 </code></pre></div> <p>我们都在使用<em>函数</em>！</p> <div class="notecard note"> <p><strong>备注：</strong> 如果需要，你可以随意将这些代码输入浏览器控制台以便于你熟悉其功能。</p> </div> <p>JavaScript 语言中有许多内置的函数，它们可以让你无需自己编写所有的代码，就能做很多有用的事情。事实上，许多你<strong>调用</strong>（专业词语，意指“运行”或“执行”）浏览器内置函数时调用的代码并不能用 JavaScript 来编写——大多数调用浏览器后台的函数的代码，是使用像 C++ 这样更低级的系统语言编写的，而不是像 JavaScript 这样的 web 编程语言。</p> <p>请记住，这些内置浏览器函数不是核心 JavaScript 语言的一部分——其中部分函数被定义为浏览器 API 的一部分，它建立在默认语言之上，以提供更多的功能（请参阅<a href="/zh-CN/docs/Learn_web_development/Core/Scripting/What_is_JavaScript#它到底可以做什么？">本课程的早期部分</a>以获得更多的描述）。我们将在以后的模块中更详细地介绍如何使用浏览器 API。</p></div></section><section aria-labelledby="函数与方法"><h2 id="函数与方法"><a href="#函数与方法">函数与方法</a></h2><div class="section-content"><p>对象的成员<strong>函数</strong>被称为<strong>方法</strong>。你还不必了解 JavaScript 中已构建的对象在更深层次上是如何运作的——你可以等到下一小节，我们会教给你有关对象运作方式的一切以及如何创建它们。在我们继续之前，我们需要澄清一些有关方法和函数概念之间可能存在的混淆——当你在网络上浏览相关信息的时候，你很可能会碰上这两个术语。</p> <p>到目前为止我们所使用的内置代码同属于这两种形式：<strong>函数</strong>和<strong>方法</strong>。你可以在<a href="/zh-CN/docs/Web/JavaScript/Reference/Global_Objects">这里</a>查看内置函数、内置对象以及其相关方法的完整列表。</p> <p>你在过去的课程中也见到过很多<strong>自定义函数</strong>——在你的代码中而非浏览器中定义的函数。每当你看到一个后面带有括号的自定义名称，那么你使用的是自定义函数。在我们的<a href="/zh-CN/docs/Learn_web_development/Core/Scripting/Loops">循环文章中</a>的 <a href="https://mdn.github.io/learning-area/javascript/building-blocks/loops/random-canvas-circles.html" class="external" target="_blank">random-canvas-circles.html</a> 示例（参见完整的<a href="https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/loops/random-canvas-circles.html" class="external" target="_blank">源代码</a>）中，我们包含一个如下所示的自定义 <code>draw()</code> 函数：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function draw() { ctx.clearRect(0, 0, WIDTH, HEIGHT); for (let i = 0; i < 100; i++) { ctx.beginPath(); ctx.fillStyle = "rgb(255 0 0 / 50%)"; ctx.arc(random(WIDTH), random(HEIGHT), random(50), 0, 2 * Math.PI); ctx.fill(); } } </code></pre></div> <p>该函数在 <a href="/zh-CN/docs/Web/HTML/Element/canvas"><code><canvas></code></a> 元素中绘制 100 个随机大小的圆。每次我们想要这样做，我们只需要调用这个函数：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>draw(); </code></pre></div> <p>而不是每次我们想要这样做，都需要写出所有的代码。函数可以包含任何你喜欢的代码——甚至可以在函数内调用其他函数。以上示例代码调用了 <code>random()</code> 函数三次，该函数由以下代码定义：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function random(number) { return Math.floor(Math.random() * number); } </code></pre></div> <p>我们需要这个函数，因为浏览器的内置 <a href="/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Math/random">Math.random()</a> 函数只生成一个 0 到 1 之间的随机十进制数。我们想要一个 0 到一个指定数字之间的随机整数。</p></div></section><section aria-labelledby="调用函数"><h2 id="调用函数"><a href="#调用函数">调用函数</a></h2><div class="section-content"><p>你现在可能很清楚这一点，但以防万一，我们还是提醒一下：要在函数定义之后实际使用它，你必须运行（或调用）它。这可以通过在代码的某个地方包含函数名，然后加上圆括号来实现。</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function myFunction() { alert("你好"); } myFunction(); // 调用一次该函数 </code></pre></div> <div class="notecard note"> <p><strong>备注：</strong> 这种创建函数的形式，也被称为<em>函数声明</em>。它总是被<a href="/zh-CN/docs/Glossary/Hoisting">提升</a>的，这样你就能在函数定义之前调用该函数。</p> </div></div></section><section aria-labelledby="函数参数"><h2 id="函数参数"><a href="#函数参数">函数参数</a></h2><div class="section-content"><p>有些函数在调用它们时需要指定<strong>参数</strong>——这些值需要放在函数括号内，函数才能正确地完成其工作。</p> <div class="notecard note"> <p><strong>备注：</strong> 参数（parameter）有时称为参数（argument）、属性（property）或甚至特性（attribute）。</p> </div> <p>例如，浏览器的内置 <a href="/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Math/random">Math.random()</a> 函数不需要任何参数。当被调用时，它总是返回 0 到 1 之间的随机数：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const myNumber = Math.random(); </code></pre></div> <p>浏览器的内置字符串 <a href="/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/String/replace">replace()</a> 函数需要两个参数：在主字符串中查找的子字符串，以及用于替换该字符串的子字符串：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const myText = "我是一个字符串"; const newString = myText.replace("字符串", "香肠"); </code></pre></div> <div class="notecard note"> <p><strong>备注：</strong> 当你需要指定多个参数时，它们以逗号分隔。</p> </div></div></section><section aria-labelledby="可选参数"><h3 id="可选参数"><a href="#可选参数">可选参数</a></h3><div class="section-content"><p>还应该注意，有时参数不是必需的——你不必指定它们。如果你没有指定某些参数，该函数一般会采用某种默认行为。例如，数组的 <a href="/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/join">join()</a> 函数的参数是可选的：</p>  <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const myArray = ["我", "爱", "巧克力", "青蛙"]; const madeAString = myArray.join(" "); console.log(madeAString); // 返回 '我爱巧克力青蛙' const madeAnotherString = myArray.join(); console.log(madeAnotherString); // 返回“我,爱,巧克力,青蛙” </code></pre></div>  <p>如果没有包含参数来指定连接/分隔符，默认情况下会使用逗号。</p></div></section><section aria-labelledby="默认参数"><h3 id="默认参数"><a href="#默认参数">默认参数</a></h3><div class="section-content"><p>如果你正在编写一个函数，并希望支持可选参数，你可以在参数名称后添加 <code>=</code>，然后再添加默认值来指定默认值：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function hello(name = "克里斯") { console.log(`你好，${name}！`); } hello("阿里"); // 你好，阿里！ hello(); // 你好，克里斯！ </code></pre></div></div></section><section aria-labelledby="匿名函数和箭头函数"><h2 id="匿名函数和箭头函数"><a href="#匿名函数和箭头函数">匿名函数和箭头函数</a></h2><div class="section-content"><p>到目前为止，我们创建了如下函数：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function myFunction() { alert("你好"); } </code></pre></div> <p>但是你也可以创建一个没有名称的函数：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>(function () { alert("你好"); }); </code></pre></div> <p>这就是所谓的<strong>匿名函数</strong>，因为它没有名字。当一个函数希望接收另一个函数作为参数时，你经常会看到匿名函数。在这种情况下，函数参数通常作为匿名函数传递。</p> <div class="notecard note"> <p><strong>备注：</strong> 这种创建函数的形式也称为<em>函数表达式</em>。与函数声明不同，函数表达式不会被<a href="/zh-CN/docs/Glossary/Hoisting">提升</a>。</p> </div></div></section><section aria-labelledby="匿名函数示例"><h3 id="匿名函数示例"><a href="#匿名函数示例">匿名函数示例</a></h3><div class="section-content"><p>例如，你想在用户输入文本框时运行一些代码。为此，你可以调用文本框的 <a href="/zh-CN/docs/Web/API/EventTarget/addEventListener" title="addEventListener()"><code>addEventListener()</code></a> 函数。该函数希望你（至少）传给它两个参数：</p> <ul> <li>要监听的事件名称，本例中为 <a href="/zh-CN/docs/Web/API/Element/keydown_event" title="keydown"><code>keydown</code></a></li> <li>事件发生时要运行的函数。</li> </ul> <p>当用户按下某个按键时，浏览器将调用你提供的函数，并传递给它一个包含该事件信息的参数，其中包括用户按下的特定按键：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function logKey(event) { console.log(`You pressed "${event.key}".`); } textBox.addEventListener("keydown", logKey); </code></pre></div> <p>你可以将一个匿名函数传入 <code>addEventListener()</code>，而不是定义一个单独的 <code>logKey()</code> 函数：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>textBox.addEventListener("keydown", function (event) { console.log(`You pressed "${event.key}".`); }); </code></pre></div></div></section><section aria-labelledby="箭头函数"><h3 id="箭头函数"><a href="#箭头函数">箭头函数</a></h3><div class="section-content"><p>如果你传递这样一个匿名函数，你可以使用另一种形式，即<strong>箭头函数</strong>。你可以用 <code>(event) =></code> 来代替 <code>function(event)</code>：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>textBox.addEventListener("keydown", (event) => { console.log(`You pressed "${event.key}".`); }); </code></pre></div> <p>如果函数只接受一个参数，可以省略参数周围的括号：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>textBox.addEventListener("keydown", event => { console.log(`You pressed "${event.key}".`); }); </code></pre></div> <p>最后，如果函数只包含一行 <code>return</code> 语句，也可以省略圆括号和 <code>return</code> 关键字，隐式地返回表达式。在下面的示例中，我们使用 <code>Array</code> 的 <a href="/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/map"><code>map()</code></a> 方法将原始数组中的每个值加倍：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const originals = [1, 2, 3]; const doubled = originals.map(item => item * 2); console.log(doubled); // [2, 4, 6] </code></pre></div> <p><code>map()</code> 方法依次获取数组中的每一项，并将其传递给给定函数。然后，它将该函数返回的值添加到一个新数组中。</p> <p>因此，在上面的例子中，箭头函数 <code>item => item * 2</code> 相当于：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function doubleItem(item) { return item * 2; } </code></pre></div> <p>你可以使用同样简洁的语法重写 <code>addEventListener</code> 示例。</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>textBox.addEventListener("keydown", (event) => console.log(`You pressed "${event.key}".`), ); </code></pre></div> <p>在这种情况下，回调函数隐式返回 <code>console.log()</code> 的值，即 <code>undefined</code>。</p> <p>我们建议你使用箭头函数，因为它们可以使你的代码更简短、更易读。要了解更多信息，请参阅 <a href="/zh-CN/docs/Web/JavaScript/Guide/Functions#箭头函数">JavaScript 指南中的有关部分</a>，以及我们<a href="/zh-CN/docs/Web/JavaScript/Reference/Functions/Arrow_functions">有关箭头函数的参考文档</a>。</p> <div class="notecard note"> <p><strong>备注：</strong> 注意：箭头函数和普通函数之间存在一些细微差别。它们超出了本入门指南的范围，并且不太可能在我们在这里讨论的案例中产生影响。要了解更多信息，请参阅<a href="/zh-CN/docs/Web/JavaScript/Reference/Functions/Arrow_functions">箭头函数参考文档</a>。</p> </div></div></section><section aria-labelledby="箭头函数实时示例"><h3 id="箭头函数实时示例"><a href="#箭头函数实时示例">箭头函数实时示例</a></h3><div class="section-content"><p>下面是我们上面讨论的“keydown”示例的完整工作示例：</p> <p>HTML 文件：</p> <div class="code-example"><div class="example-header"><span class="language-name">html</span></div><pre class="brush: html notranslate"><code><input id="textBox" type="text" /> <div id="output"></div> </code></pre></div> <p>JavaScript 文件：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const textBox = document.querySelector("#textBox"); const output = document.querySelector("#output"); textBox.addEventListener("keydown", (event) => { output.textContent = `You pressed "${event.key}".`; }); </code></pre></div> <div class="code-example"><pre class="brush: css hidden notranslate"><code>div { margin: 0.5rem 0; } </code></pre></div> <p>结果——试着输入文本框，看看输出结果：</p> <div class="code-example"><div class="example-header"></div><iframe class="sample-code-frame" title="箭头函数实时示例 sample" id="frame_箭头函数实时示例" width="100" height="100" src="about:blank" data-live-path="/zh-CN/docs/Learn_web_development/Core/Scripting/Functions/" data-live-id="箭头函数实时示例" sandbox="allow-same-origin allow-scripts" loading="lazy"></iframe></div></div></section><section aria-labelledby="函数作用域和冲突"><h2 id="函数作用域和冲突"><a href="#函数作用域和冲突">函数作用域和冲突</a></h2><div class="section-content"><p>我们来谈一谈<a href="/zh-CN/docs/Glossary/Scope">作用域</a>——处理函数时一个非常重要的概念。当你创建一个函数时，函数内定义的变量和其他东西都在它们自己的单独的<strong>作用域</strong>内，意味着它们被锁在自己独立的隔间中，不能被函数外的代码访问。</p> <p>所有函数的最外层被称为<strong>全局作用域</strong>。在全局作用域内定义的值可以在任意地方访问。</p> <p>JavaScript 之所以设计成如此，有很多原因，但主要是出于安全性和组织性的考虑。有时你不希望变量可以在代码中的任何地方被访问到——你从其他地方调用的外部脚本可能会开始干扰你的代码并导致问题，因为它们可能与代码的其它部分使用了相同的变量名称，造成冲突。这可能是出于恶意目的，或者只是意外。</p> <p>例如，假设你有一个 HTML 文件，它调用两个外部 JavaScript 文件，并且它们都有一个使用相同名称定义的变量和函数：</p> <div class="code-example"><div class="example-header"><span class="language-name">html</span></div><pre class="brush: html notranslate"><code> <script src="first.js"></script> <script src="second.js"></script> <script> greeting(); </script> </code></pre></div> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>// first.js const name = "Chris"; function greeting() { alert(`Hello ${name}: welcome to our company.`); } </code></pre></div> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>// second.js const name = "Zaptec"; function greeting() { alert(`Our company is called ${name}.`); } </code></pre></div> <p>你想要调用的两个函数都被命名为 <code>greeting()</code>，但你只能访问到 <code>first.js</code> 文件中的 <code>greeting()</code> 函数（第二个函数会被忽略）。此外，（在 <code>second.js</code> 文件中）试图给 <code>name</code> 变量赋一个新值时会导致错误，因为它已经用 <code>const</code> 声明过了，所以无法重新赋值。</p> <div class="notecard note"> <p><strong>备注：</strong> 你可以<a href="https://mdn.github.io/learning-area/javascript/building-blocks/functions/conflict.html" class="external" target="_blank">在 GitHub 上参考运行的实例</a>（查看完整<a href="https://github.com/mdn/learning-area/tree/main/javascript/building-blocks/functions" class="external" target="_blank">源代码</a>）。</p> </div> <p>将部分代码锁定在函数中避免了这样的问题，并被认为是最佳实践。</p> <p>这有点像一个动物园。狮子、斑马、老虎和企鹅都保留在自己的园子中，只能拿到到它们园子中的东西——与其函数作用域相同。如果他们能进入其他园子，就会出现问题。不同的动物会在不熟悉的栖息地内感到真的不舒服——一只狮子或老虎会在企鹅的水多的，冰冷的领域中感到可怕。最糟糕的是，狮子和老虎可能会尝试吃企鹅！</p> <p><img src="/zh-CN/docs/Learn_web_development/Core/Scripting/Functions/mdn-mozilla-zoo.png" alt="四种不同的动物被封闭在动物园各自的栖息地中" width="656" height="416" loading="lazy"></p> <p>动物园管理员就像全局作用域——他或她有钥匙访问每个园子，重新投喂食物，照顾生病的动物等。</p></div></section><section aria-labelledby="主动学习：和_scope_玩耍"><h3 id="主动学习：和_scope_玩耍"><a href="#主动学习：和_scope_玩耍">主动学习：和 scope 玩耍</a></h3><div class="section-content"><p>我们来看一个真正的例子来展示范围</p> <ol> <li> <p>首先，创建我们的 <a href="https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/functions/function-scope.html" class="external" target="_blank">function-scope.html</a> 示例的本地副本。它包含两个函数 <code>a()</code> 和 <code>b()</code>，和三个变量——<code>x</code>、<code>y</code>和<code>z</code>——其中两个在函数中被定义，另一个被定义在全局作用域内。它还包含一个名为 <code>output()</code> 的函数，它接收一个参数，并将其输出到页面的一个段落中。</p> </li> <li> <p>在浏览器和文本编辑器中打开示例。</p> </li> <li> <p>在浏览器开发工具中打开 JavaScript 控制台。在 JavaScript 控制台中，输入以下命令：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>output(x); </code></pre></div> <p>你应该看到变量 <code>x</code> 输出到屏幕的值。</p> </li> <li> <p>现在尝试在你的控制台中输入以下内容</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>output(y); output(z); </code></pre></div> <p>这两个都应该返回错误“<a href="/zh-CN/docs/Web/JavaScript/Reference/Errors/Not_defined">ReferenceError：y is not defined</a>”。这是为什么？这是因为函数作用域——<code>y</code> 和 <code>z</code> 被限制在函数 <code>a()</code> 和 <code>b()</code> 函数中，所以 <code>output()</code> 从全局作用域调用时无法访问它们。</p> </li> <li> <p>但是，从另一个函数里面调用什么呢？尝试编辑 <code>a()</code>、<code>b()</code> 所以它们看起来像这样：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function a() { const y = 2; output(y); } function b() { const z = 3; output(z); } </code></pre></div> <p>保存代码并重新加载到浏览器中，然后尝试从 JavaScript 控制台调用 <code>a()</code> 和 <code>b()</code> 函数：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>a(); b(); </code></pre></div> <p>你应该看到页面中输出的 <code>y</code> 和 <code>z</code> 的值。这样就没问题，因为 <code>output()</code> 函数在其他函数的内部被调用——在这种情况下，输出变量的定义和函数的调用都在同一个作用域中。<code>output()</code> 它可以从任何地方被调用，因为它在全局作用域中被定义。</p> </li> <li> <p>现在尝试更新你的代码，如下所示：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function a() { const y = 2; output(x); } function b() { const z = 3; output(x); } </code></pre></div> </li> <li> <p>再次保存并重新加载，并在 JavaScript 控制台中再次尝试：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>a(); b(); </code></pre></div> <p>函数 <code>a()</code> 和 <code>b()</code> 都应该输出 <code>x</code> 的值。这些没有问题，因为即使 <code>output()</code> 的调用与 <code>x</code> 的定义不在同一个作用域内，但 <code>x</code> 是一个全局变量，所以在所有代码中都可用。</p> </li> <li> <p>最后，尝试更新你的代码，如下所示：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function a() { const y = 2; output(z); } function b() { const z = 3; output(y); } </code></pre></div> </li> <li> <p>再次保存并重新加载，并在 JavaScript 控制台中再次尝试：</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>a(); b(); </code></pre></div> <p>这次 <code>a()</code> 和 <code>b()</code> 调用都会返回那个令人讨厌的“<a href="/zh-CN/docs/Web/JavaScript/Reference/Errors/Not_defined">ReferenceError: <em>variable name</em> is not defined</a>”错误——这是因为 <code>output()</code> 函数的调用和输出变量的定义不在同一个函数作用域内——变量对于这些函数调用而言是不可见的。</p> </li> </ol> <div class="notecard note"> <p><strong>备注：</strong> 相同的作用域规则不适用于循环（例如 <code>for() { }</code>）和条件块（例如 <code>if() { }</code>）——它们看起来非常相似，但它们不一样！千万不要混淆它们。</p> </div> <div class="notecard note"> <p><strong>备注：</strong> “<a href="/zh-CN/docs/Web/JavaScript/Reference/Errors/Not_defined">ReferenceError: "x" is not defined</a>”错误将会是你遇到的最常见的错误。如果你收到此错误，并且确定你已经定义了该变量，请检查它的作用域。</p> </div></div></section><section aria-labelledby="技能测试！"><h2 id="技能测试！"><a href="#技能测试！">技能测试！</a></h2><div class="section-content"><p>你已经来到了本文章的结尾，但是你还能记得最重要的知识吗？你可以在离开这里找到一些更深度的测试来证实你已经记住了这些知识——查看<a href="/en-US/docs/Learn_web_development/Core/Scripting/Test_your_skills:_Functions" class="only-in-en-us">技能测试：函数</a>。后两章文本包含了这个测试需要的技能，所以你可能先需要阅读再尝试该测试。</p></div></section><section aria-labelledby="总结"><h2 id="总结"><a href="#总结">总结</a></h2><div class="section-content"><p>本文探讨了函数背后的基本概念，为之后的学习奠定了基础。下一步，我们将进行实践，并带你一步步建立起你自己的函数。</p></div></section><section aria-labelledby="参见"><h2 id="参见"><a href="#参见">参见</a></h2><div class="section-content"><ul> <li><a href="/zh-CN/docs/Web/JavaScript/Guide/Functions">函数的详细指南</a>——涵盖了此处未包含的一些高级特性。</li> <li><a href="/zh-CN/docs/Web/JavaScript/Reference/Functions">函数参考</a></li> <li><a href="/zh-CN/docs/Web/JavaScript/Reference/Functions/Default_parameters">默认参数</a>、<a href="/zh-CN/docs/Web/JavaScript/Reference/Functions/Arrow_functions">箭头函数</a>——高级概念参考</li> </ul> <ul class="prev-next"><li><a class="button secondary" href="/zh-CN/docs/Learn_web_development/Core/Scripting/Loops"><span class="button-wrap"> 上一页 </span></a></li><li><a class="button secondary" href="/zh-CN/docs/Learn_web_development/Core/Scripting"><span class="button-wrap"> 概述：创建 JavaScript 代码块</span></a></li><li><a class="button secondary" href="/zh-CN/docs/Learn_web_development/Core/Scripting/Build_your_own_function"><span class="button-wrap"> 下一页 </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" 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noreferrer">Website Privacy Notice</a></li><li class="footer-moz-item"><a href="https://www.mozilla.org/privacy/websites/#cookies" 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="/zh-CN/docs/MDN/Writing_guidelines/Attrib_copyright_license">a Creative Commons license</a>.</p></div></div></footer></div><script type="application/json" id="hydration">{"url":"/zh-CN/docs/Learn_web_development/Core/Scripting/Functions","doc":{"body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<ul class=\"prev-next\"><li><a class=\"button secondary\" href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Loops\"><span class=\"button-wrap\"> 上一页 </span></a></li><li><a class=\"button secondary\" href=\"/zh-CN/docs/Learn_web_development/Core/Scripting\"><span class=\"button-wrap\"> 概述：创建 JavaScript 代码块</span></a></li><li><a class=\"button secondary\" href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Build_your_own_function\"><span class=\"button-wrap\"> 下一页 </span></a></li></ul>\n<p>在 JavaScript 中另一个基本概念是<strong>函数</strong>, 它允许你在一个代码块中存储一段用于处理单任务的代码，然后在任何你需要的时候用一个简短的命令来调用，而不是把相同的代码写很多次。在本文中，我们将探索函数的基本概念，如函数的基本语法、如何定义和调用函数、函数的作用域和参数。</p>\n<figure class=\"table-container\"><table>\n <tbody>\n <tr>\n <th scope=\"row\">前提：</th>\n <td>\n 基本的电脑知识，对 HTML 与 CSS 有基本的了解，及已阅读：<a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting\">JavaScript 第一步</a>。\n </td>\n </tr>\n <tr>\n <th scope=\"row\">目标：</th>\n <td>了解 Javascript 函数背后的基本概念。</td>\n </tr>\n </tbody>\n</table></figure>"}},{"type":"prose","value":{"id":"我能在哪找到函数？","title":"我能在哪找到函数？","isH3":false,"content":"<p>在 JavaScript 中，你将发现函数无处不在。事实上，到目前为止，我们一直在使用函数；我们只是还没正式地讨论它们。然而现在是时候了，让我们开始聊聊函数，并探索它们的语法。</p>\n<p>几乎任何时候，只要你使用一个带有一对圆括号（<code>()</code>）的 JavaScript 结构，并且你<strong>没有</strong>使用比如 <a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Loops#循环的标准\">for 循环</a>、<a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Loops#while_语句和_do_..._while_语句\">while 或 do...while 循环</a>，或者 <a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Conditionals#if...else_语句\">if...else 语句</a>这样的常见的内置语言结构时，那么你就正在使用函数。</p>"}},{"type":"prose","value":{"id":"浏览器内置函数","title":"浏览器内置函数","isH3":false,"content":"<p>在这套课程中我们已经使用了很多浏览器内置函数。</p>\n<p>例如，当我们操作一个字符串的时候：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const myText = \"我是一个字符串\";\nconst newString = myText.replace(\"字符串\", \"香肠\");\nconsole.log(newString);\n// replace() 字符串函数接受源字符串和目标字符串，\n// 将源字符串替换为目标字符串，并返回新形成的字符串\n</code></pre></div>\n<p>或者当我们操作一个数组的时候：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const myArray = [\"我\", \"爱\", \"巧克力\", \"青蛙\"];\nconst madeAString = myArray.join(\" \");\nconsole.log(madeAString);\n// join() 函数接受一个数组，\n// 将所有数组元素连接成一个单一的字符串，并返回这个新字符串\n</code></pre></div>\n<p>或者当我们生成一个随机数时：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const myNumber = Math.random();\n// random() 函数生成一个随机\n// 数字在 0 和 1 之间，并返回该数字\n</code></pre></div>\n<p>我们都在使用<em>函数</em>！</p>\n<div class=\"notecard note\">\n<p><strong>备注：</strong>\n如果需要，你可以随意将这些代码输入浏览器控制台以便于你熟悉其功能。</p>\n</div>\n<p>JavaScript 语言中有许多内置的函数，它们可以让你无需自己编写所有的代码，就能做很多有用的事情。事实上，许多你<strong>调用</strong>（专业词语，意指“运行”或“执行”）浏览器内置函数时调用的代码并不能用 JavaScript 来编写——大多数调用浏览器后台的函数的代码，是使用像 C++ 这样更低级的系统语言编写的，而不是像 JavaScript 这样的 web 编程语言。</p>\n<p>请记住，这些内置浏览器函数不是核心 JavaScript 语言的一部分——其中部分函数被定义为浏览器 API 的一部分，它建立在默认语言之上，以提供更多的功能（请参阅<a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/What_is_JavaScript#它到底可以做什么？\">本课程的早期部分</a>以获得更多的描述）。我们将在以后的模块中更详细地介绍如何使用浏览器 API。</p>"}},{"type":"prose","value":{"id":"函数与方法","title":"函数与方法","isH3":false,"content":"<p>对象的成员<strong>函数</strong>被称为<strong>方法</strong>。你还不必了解 JavaScript 中已构建的对象在更深层次上是如何运作的——你可以等到下一小节，我们会教给你有关对象运作方式的一切以及如何创建它们。在我们继续之前，我们需要澄清一些有关方法和函数概念之间可能存在的混淆——当你在网络上浏览相关信息的时候，你很可能会碰上这两个术语。</p>\n<p>到目前为止我们所使用的内置代码同属于这两种形式：<strong>函数</strong>和<strong>方法</strong>。你可以在<a href=\"/zh-CN/docs/Web/JavaScript/Reference/Global_Objects\">这里</a>查看内置函数、内置对象以及其相关方法的完整列表。</p>\n<p>你在过去的课程中也见到过很多<strong>自定义函数</strong>——在你的代码中而非浏览器中定义的函数。每当你看到一个后面带有括号的自定义名称，那么你使用的是自定义函数。在我们的<a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Loops\">循环文章中</a>的 <a href=\"https://mdn.github.io/learning-area/javascript/building-blocks/loops/random-canvas-circles.html\" class=\"external\" target=\"_blank\">random-canvas-circles.html</a> 示例（参见完整的<a href=\"https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/loops/random-canvas-circles.html\" class=\"external\" target=\"_blank\">源代码</a>）中，我们包含一个如下所示的自定义 <code>draw()</code> 函数：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function draw() {\n ctx.clearRect(0, 0, WIDTH, HEIGHT);\n for (let i = 0; i < 100; i++) {\n ctx.beginPath();\n ctx.fillStyle = \"rgb(255 0 0 / 50%)\";\n ctx.arc(random(WIDTH), random(HEIGHT), random(50), 0, 2 * Math.PI);\n ctx.fill();\n }\n}\n</code></pre></div>\n<p>该函数在 <a href=\"/zh-CN/docs/Web/HTML/Element/canvas\"><code><canvas></code></a> 元素中绘制 100 个随机大小的圆。每次我们想要这样做，我们只需要调用这个函数：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>draw();\n</code></pre></div>\n<p>而不是每次我们想要这样做，都需要写出所有的代码。函数可以包含任何你喜欢的代码——甚至可以在函数内调用其他函数。以上示例代码调用了 <code>random()</code> 函数三次，该函数由以下代码定义：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function random(number) {\n return Math.floor(Math.random() * number);\n}\n</code></pre></div>\n<p>我们需要这个函数，因为浏览器的内置 <a href=\"/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Math/random\">Math.random()</a> 函数只生成一个 0 到 1 之间的随机十进制数。我们想要一个 0 到一个指定数字之间的随机整数。</p>"}},{"type":"prose","value":{"id":"调用函数","title":"调用函数","isH3":false,"content":"<p>你现在可能很清楚这一点，但以防万一，我们还是提醒一下：要在函数定义之后实际使用它，你必须运行（或调用）它。这可以通过在代码的某个地方包含函数名，然后加上圆括号来实现。</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function myFunction() {\n alert(\"你好\");\n}\n\nmyFunction();\n// 调用一次该函数\n</code></pre></div>\n<div class=\"notecard note\">\n<p><strong>备注：</strong>\n这种创建函数的形式，也被称为<em>函数声明</em>。它总是被<a href=\"/zh-CN/docs/Glossary/Hoisting\">提升</a>的，这样你就能在函数定义之前调用该函数。</p>\n</div>"}},{"type":"prose","value":{"id":"函数参数","title":"函数参数","isH3":false,"content":"<p>有些函数在调用它们时需要指定<strong>参数</strong>——这些值需要放在函数括号内，函数才能正确地完成其工作。</p>\n<div class=\"notecard note\">\n<p><strong>备注：</strong>\n参数（parameter）有时称为参数（argument）、属性（property）或甚至特性（attribute）。</p>\n</div>\n<p>例如，浏览器的内置 <a href=\"/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Math/random\">Math.random()</a> 函数不需要任何参数。当被调用时，它总是返回 0 到 1 之间的随机数：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const myNumber = Math.random();\n</code></pre></div>\n<p>浏览器的内置字符串 <a href=\"/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/String/replace\">replace()</a> 函数需要两个参数：在主字符串中查找的子字符串，以及用于替换该字符串的子字符串：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const myText = \"我是一个字符串\";\nconst newString = myText.replace(\"字符串\", \"香肠\");\n</code></pre></div>\n<div class=\"notecard note\">\n<p><strong>备注：</strong>\n当你需要指定多个参数时，它们以逗号分隔。</p>\n</div>"}},{"type":"prose","value":{"id":"可选参数","title":"可选参数","isH3":true,"content":"<p>还应该注意，有时参数不是必需的——你不必指定它们。如果你没有指定某些参数，该函数一般会采用某种默认行为。例如，数组的 <a href=\"/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/join\">join()</a> 函数的参数是可选的：</p>\n\u003c!-- autocorrect-disable -->\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const myArray = [\"我\", \"爱\", \"巧克力\", \"青蛙\"];\nconst madeAString = myArray.join(\" \");\nconsole.log(madeAString);\n// 返回 '我爱巧克力青蛙'\n\nconst madeAnotherString = myArray.join();\nconsole.log(madeAnotherString);\n// 返回“我,爱,巧克力,青蛙”\n</code></pre></div>\n\u003c!-- autocorrect-enable -->\n<p>如果没有包含参数来指定连接/分隔符，默认情况下会使用逗号。</p>"}},{"type":"prose","value":{"id":"默认参数","title":"默认参数","isH3":true,"content":"<p>如果你正在编写一个函数，并希望支持可选参数，你可以在参数名称后添加 <code>=</code>，然后再添加默认值来指定默认值：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function hello(name = \"克里斯\") {\n console.log(`你好，${name}！`);\n}\n\nhello(\"阿里\"); // 你好，阿里！\nhello(); // 你好，克里斯！\n</code></pre></div>"}},{"type":"prose","value":{"id":"匿名函数和箭头函数","title":"匿名函数和箭头函数","isH3":false,"content":"<p>到目前为止，我们创建了如下函数：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function myFunction() {\n alert(\"你好\");\n}\n</code></pre></div>\n<p>但是你也可以创建一个没有名称的函数：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>(function () {\n alert(\"你好\");\n});\n</code></pre></div>\n<p>这就是所谓的<strong>匿名函数</strong>，因为它没有名字。当一个函数希望接收另一个函数作为参数时，你经常会看到匿名函数。在这种情况下，函数参数通常作为匿名函数传递。</p>\n<div class=\"notecard note\">\n<p><strong>备注：</strong>\n这种创建函数的形式也称为<em>函数表达式</em>。与函数声明不同，函数表达式不会被<a href=\"/zh-CN/docs/Glossary/Hoisting\">提升</a>。</p>\n</div>"}},{"type":"prose","value":{"id":"匿名函数示例","title":"匿名函数示例","isH3":true,"content":"<p>例如，你想在用户输入文本框时运行一些代码。为此，你可以调用文本框的 <a href=\"/zh-CN/docs/Web/API/EventTarget/addEventListener\" title=\"addEventListener()\"><code>addEventListener()</code></a> 函数。该函数希望你（至少）传给它两个参数：</p>\n<ul>\n<li>要监听的事件名称，本例中为 <a href=\"/zh-CN/docs/Web/API/Element/keydown_event\" title=\"keydown\"><code>keydown</code></a></li>\n<li>事件发生时要运行的函数。</li>\n</ul>\n<p>当用户按下某个按键时，浏览器将调用你提供的函数，并传递给它一个包含该事件信息的参数，其中包括用户按下的特定按键：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function logKey(event) {\n console.log(`You pressed \"${event.key}\".`);\n}\n\ntextBox.addEventListener(\"keydown\", logKey);\n</code></pre></div>\n<p>你可以将一个匿名函数传入 <code>addEventListener()</code>，而不是定义一个单独的 <code>logKey()</code> 函数：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>textBox.addEventListener(\"keydown\", function (event) {\n console.log(`You pressed \"${event.key}\".`);\n});\n</code></pre></div>"}},{"type":"prose","value":{"id":"箭头函数","title":"箭头函数","isH3":true,"content":"<p>如果你传递这样一个匿名函数，你可以使用另一种形式，即<strong>箭头函数</strong>。你可以用 <code>(event) =></code> 来代替 <code>function(event)</code>：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>textBox.addEventListener(\"keydown\", (event) => {\n console.log(`You pressed \"${event.key}\".`);\n});\n</code></pre></div>\n<p>如果函数只接受一个参数，可以省略参数周围的括号：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>textBox.addEventListener(\"keydown\", event => {\n console.log(`You pressed \"${event.key}\".`);\n});\n</code></pre></div>\n<p>最后，如果函数只包含一行 <code>return</code> 语句，也可以省略圆括号和 <code>return</code> 关键字，隐式地返回表达式。在下面的示例中，我们使用 <code>Array</code> 的 <a href=\"/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/map\"><code>map()</code></a> 方法将原始数组中的每个值加倍：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const originals = [1, 2, 3];\n\nconst doubled = originals.map(item => item * 2);\n\nconsole.log(doubled); // [2, 4, 6]\n</code></pre></div>\n<p><code>map()</code> 方法依次获取数组中的每一项，并将其传递给给定函数。然后，它将该函数返回的值添加到一个新数组中。</p>\n<p>因此，在上面的例子中，箭头函数 <code>item => item * 2</code> 相当于：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function doubleItem(item) {\n return item * 2;\n}\n</code></pre></div>\n<p>你可以使用同样简洁的语法重写 <code>addEventListener</code> 示例。</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>textBox.addEventListener(\"keydown\", (event) =>\n console.log(`You pressed \"${event.key}\".`),\n);\n</code></pre></div>\n<p>在这种情况下，回调函数隐式返回 <code>console.log()</code> 的值，即 <code>undefined</code>。</p>\n<p>我们建议你使用箭头函数，因为它们可以使你的代码更简短、更易读。要了解更多信息，请参阅 <a href=\"/zh-CN/docs/Web/JavaScript/Guide/Functions#箭头函数\">JavaScript 指南中的有关部分</a>，以及我们<a href=\"/zh-CN/docs/Web/JavaScript/Reference/Functions/Arrow_functions\">有关箭头函数的参考文档</a>。</p>\n<div class=\"notecard note\">\n<p><strong>备注：</strong>\n注意：箭头函数和普通函数之间存在一些细微差别。它们超出了本入门指南的范围，并且不太可能在我们在这里讨论的案例中产生影响。要了解更多信息，请参阅<a href=\"/zh-CN/docs/Web/JavaScript/Reference/Functions/Arrow_functions\">箭头函数参考文档</a>。</p>\n</div>"}},{"type":"prose","value":{"id":"箭头函数实时示例","title":"箭头函数实时示例","isH3":true,"content":"<p>下面是我们上面讨论的“keydown”示例的完整工作示例：</p>\n<p>HTML 文件：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">html</span></div><pre class=\"brush: html notranslate\"><code><input id=\"textBox\" type=\"text\" />\n<div id=\"output\"></div>\n</code></pre></div>\n<p>JavaScript 文件：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const textBox = document.querySelector(\"#textBox\");\nconst output = document.querySelector(\"#output\");\n\ntextBox.addEventListener(\"keydown\", (event) => {\n output.textContent = `You pressed \"${event.key}\".`;\n});\n</code></pre></div>\n<div class=\"code-example\"><pre class=\"brush: css hidden notranslate\"><code>div {\n margin: 0.5rem 0;\n}\n</code></pre></div>\n<p>结果——试着输入文本框，看看输出结果：</p>\n<div class=\"code-example\"><div class=\"example-header\"></div><iframe class=\"sample-code-frame\" title=\"箭头函数实时示例 sample\" id=\"frame_箭头函数实时示例\" width=\"100\" height=\"100\" src=\"about:blank\" data-live-path=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Functions/\" data-live-id=\"箭头函数实时示例\" sandbox=\"allow-same-origin allow-scripts\" loading=\"lazy\"></iframe></div>"}},{"type":"prose","value":{"id":"函数作用域和冲突","title":"函数作用域和冲突","isH3":false,"content":"<p>我们来谈一谈<a href=\"/zh-CN/docs/Glossary/Scope\">作用域</a>——处理函数时一个非常重要的概念。当你创建一个函数时，函数内定义的变量和其他东西都在它们自己的单独的<strong>作用域</strong>内，意味着它们被锁在自己独立的隔间中，不能被函数外的代码访问。</p>\n<p>所有函数的最外层被称为<strong>全局作用域</strong>。在全局作用域内定义的值可以在任意地方访问。</p>\n<p>JavaScript 之所以设计成如此，有很多原因，但主要是出于安全性和组织性的考虑。有时你不希望变量可以在代码中的任何地方被访问到——你从其他地方调用的外部脚本可能会开始干扰你的代码并导致问题，因为它们可能与代码的其它部分使用了相同的变量名称，造成冲突。这可能是出于恶意目的，或者只是意外。</p>\n<p>例如，假设你有一个 HTML 文件，它调用两个外部 JavaScript 文件，并且它们都有一个使用相同名称定义的变量和函数：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">html</span></div><pre class=\"brush: html notranslate\"><code>\n<script src=\"first.js\"></script>\n<script src=\"second.js\"></script>\n<script>\n greeting();\n</script>\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>// first.js\nconst name = \"Chris\";\nfunction greeting() {\n alert(`Hello ${name}: welcome to our company.`);\n}\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>// second.js\nconst name = \"Zaptec\";\nfunction greeting() {\n alert(`Our company is called ${name}.`);\n}\n</code></pre></div>\n<p>你想要调用的两个函数都被命名为 <code>greeting()</code>，但你只能访问到 <code>first.js</code> 文件中的 <code>greeting()</code> 函数（第二个函数会被忽略）。此外，（在 <code>second.js</code> 文件中）试图给 <code>name</code> 变量赋一个新值时会导致错误，因为它已经用 <code>const</code> 声明过了，所以无法重新赋值。</p>\n<div class=\"notecard note\">\n<p><strong>备注：</strong>\n你可以<a href=\"https://mdn.github.io/learning-area/javascript/building-blocks/functions/conflict.html\" class=\"external\" target=\"_blank\">在 GitHub 上参考运行的实例</a>（查看完整<a href=\"https://github.com/mdn/learning-area/tree/main/javascript/building-blocks/functions\" class=\"external\" target=\"_blank\">源代码</a>）。</p>\n</div>\n<p>将部分代码锁定在函数中避免了这样的问题，并被认为是最佳实践。</p>\n<p>这有点像一个动物园。狮子、斑马、老虎和企鹅都保留在自己的园子中，只能拿到到它们园子中的东西——与其函数作用域相同。如果他们能进入其他园子，就会出现问题。不同的动物会在不熟悉的栖息地内感到真的不舒服——一只狮子或老虎会在企鹅的水多的，冰冷的领域中感到可怕。最糟糕的是，狮子和老虎可能会尝试吃企鹅！</p>\n<p><img src=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Functions/mdn-mozilla-zoo.png\" alt=\"四种不同的动物被封闭在动物园各自的栖息地中\" width=\"656\" height=\"416\" loading=\"lazy\"></p>\n<p>动物园管理员就像全局作用域——他或她有钥匙访问每个园子，重新投喂食物，照顾生病的动物等。</p>"}},{"type":"prose","value":{"id":"主动学习：和_scope_玩耍","title":"主动学习：和 scope 玩耍","isH3":true,"content":"<p>我们来看一个真正的例子来展示范围</p>\n<ol>\n<li>\n<p>首先，创建我们的 <a href=\"https://github.com/mdn/learning-area/blob/main/javascript/building-blocks/functions/function-scope.html\" class=\"external\" target=\"_blank\">function-scope.html</a> 示例的本地副本。它包含两个函数 <code>a()</code> 和 <code>b()</code>，和三个变量——<code>x</code>、<code>y</code>和<code>z</code>——其中两个在函数中被定义，另一个被定义在全局作用域内。它还包含一个名为 <code>output()</code> 的函数，它接收一个参数，并将其输出到页面的一个段落中。</p>\n</li>\n<li>\n<p>在浏览器和文本编辑器中打开示例。</p>\n</li>\n<li>\n<p>在浏览器开发工具中打开 JavaScript 控制台。在 JavaScript 控制台中，输入以下命令：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>output(x);\n</code></pre></div>\n<p>你应该看到变量 <code>x</code> 输出到屏幕的值。</p>\n</li>\n<li>\n<p>现在尝试在你的控制台中输入以下内容</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>output(y);\noutput(z);\n</code></pre></div>\n<p>这两个都应该返回错误“<a href=\"/zh-CN/docs/Web/JavaScript/Reference/Errors/Not_defined\">ReferenceError：y is not defined</a>”。这是为什么？这是因为函数作用域——<code>y</code> 和 <code>z</code> 被限制在函数 <code>a()</code> 和 <code>b()</code> 函数中，所以 <code>output()</code> 从全局作用域调用时无法访问它们。</p>\n</li>\n<li>\n<p>但是，从另一个函数里面调用什么呢？尝试编辑 <code>a()</code>、<code>b()</code> 所以它们看起来像这样：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function a() {\n const y = 2;\n output(y);\n}\n\nfunction b() {\n const z = 3;\n output(z);\n}\n</code></pre></div>\n<p>保存代码并重新加载到浏览器中，然后尝试从 JavaScript 控制台调用 <code>a()</code> 和 <code>b()</code> 函数：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>a();\nb();\n</code></pre></div>\n<p>你应该看到页面中输出的 <code>y</code> 和 <code>z</code> 的值。这样就没问题，因为 <code>output()</code> 函数在其他函数的内部被调用——在这种情况下，输出变量的定义和函数的调用都在同一个作用域中。<code>output()</code> 它可以从任何地方被调用，因为它在全局作用域中被定义。</p>\n</li>\n<li>\n<p>现在尝试更新你的代码，如下所示：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function a() {\n const y = 2;\n output(x);\n}\n\nfunction b() {\n const z = 3;\n output(x);\n}\n</code></pre></div>\n</li>\n<li>\n<p>再次保存并重新加载，并在 JavaScript 控制台中再次尝试：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>a();\nb();\n</code></pre></div>\n<p>函数 <code>a()</code> 和 <code>b()</code> 都应该输出 <code>x</code> 的值。这些没有问题，因为即使 <code>output()</code> 的调用与 <code>x</code> 的定义不在同一个作用域内，但 <code>x</code> 是一个全局变量，所以在所有代码中都可用。</p>\n</li>\n<li>\n<p>最后，尝试更新你的代码，如下所示：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function a() {\n const y = 2;\n output(z);\n}\n\nfunction b() {\n const z = 3;\n output(y);\n}\n</code></pre></div>\n</li>\n<li>\n<p>再次保存并重新加载，并在 JavaScript 控制台中再次尝试：</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>a();\nb();\n</code></pre></div>\n<p>这次 <code>a()</code> 和 <code>b()</code> 调用都会返回那个令人讨厌的“<a href=\"/zh-CN/docs/Web/JavaScript/Reference/Errors/Not_defined\">ReferenceError: <em>variable name</em> is not defined</a>”错误——这是因为 <code>output()</code> 函数的调用和输出变量的定义不在同一个函数作用域内——变量对于这些函数调用而言是不可见的。</p>\n</li>\n</ol>\n<div class=\"notecard note\">\n<p><strong>备注：</strong>\n相同的作用域规则不适用于循环（例如 <code>for() { }</code>）和条件块（例如 <code>if() { }</code>）——它们看起来非常相似，但它们不一样！千万不要混淆它们。</p>\n</div>\n<div class=\"notecard note\">\n<p><strong>备注：</strong>\n“<a href=\"/zh-CN/docs/Web/JavaScript/Reference/Errors/Not_defined\">ReferenceError: \"x\" is not defined</a>”错误将会是你遇到的最常见的错误。如果你收到此错误，并且确定你已经定义了该变量，请检查它的作用域。</p>\n</div>"}},{"type":"prose","value":{"id":"技能测试！","title":"技能测试！","isH3":false,"content":"<p>你已经来到了本文章的结尾，但是你还能记得最重要的知识吗？你可以在离开这里找到一些更深度的测试来证实你已经记住了这些知识——查看<a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Test_your_skills:_Functions\" class=\"only-in-en-us\">技能测试：函数</a>。后两章文本包含了这个测试需要的技能，所以你可能先需要阅读再尝试该测试。</p>"}},{"type":"prose","value":{"id":"总结","title":"总结","isH3":false,"content":"<p>本文探讨了函数背后的基本概念，为之后的学习奠定了基础。下一步，我们将进行实践，并带你一步步建立起你自己的函数。</p>"}},{"type":"prose","value":{"id":"参见","title":"参见","isH3":false,"content":"<ul>\n<li><a href=\"/zh-CN/docs/Web/JavaScript/Guide/Functions\">函数的详细指南</a>——涵盖了此处未包含的一些高级特性。</li>\n<li><a href=\"/zh-CN/docs/Web/JavaScript/Reference/Functions\">函数参考</a></li>\n<li><a href=\"/zh-CN/docs/Web/JavaScript/Reference/Functions/Default_parameters\">默认参数</a>、<a href=\"/zh-CN/docs/Web/JavaScript/Reference/Functions/Arrow_functions\">箭头函数</a>——高级概念参考</li>\n</ul>\n<ul class=\"prev-next\"><li><a class=\"button secondary\" href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Loops\"><span class=\"button-wrap\"> 上一页 </span></a></li><li><a class=\"button secondary\" href=\"/zh-CN/docs/Learn_web_development/Core/Scripting\"><span class=\"button-wrap\"> 概述：创建 JavaScript 代码块</span></a></li><li><a class=\"button secondary\" href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Build_your_own_function\"><span class=\"button-wrap\"> 下一页 </span></a></li></ul>"}}],"isActive":true,"isMarkdown":true,"isTranslated":true,"locale":"zh-CN","mdn_url":"/zh-CN/docs/Learn_web_development/Core/Scripting/Functions","modified":"2024-12-21T13:03:41.000Z","native":"中文 (简体)","noIndexing":false,"other_translations":[{"locale":"en-US","title":"Functions — reusable blocks of code","native":"English (US)"},{"locale":"de","title":"Funktionen — wiederverwendbare Codeblöcke","native":"Deutsch"},{"locale":"fr","title":"Fonctions — des blocs de code réutilisables","native":"Français"},{"locale":"ja","title":"関数 — 再利用可能なコードブロック","native":"日本語"},{"locale":"ko","title":"함수 — 코드 재사용","native":"한국어"},{"locale":"pt-BR","title":"Funções — blocos reutilizáveis de código","native":"Português (do Brasil)"},{"locale":"ru","title":"Функции — Переиспользуемые блоки кода","native":"Русский"},{"locale":"zh-TW","title":"函數 - 可重複使用的程式碼區塊","native":"正體中文 (繁體)"}],"pageTitle":"函数——可复用的代码块 - 学习 Web 开发 | MDN","parents":[{"uri":"/zh-CN/docs/Learn_web_development","title":"学习 Web 开发"},{"uri":"/en-US/docs/Learn_web_development/Core","title":"Core learning modules"},{"uri":"/zh-CN/docs/Learn_web_development/Core/Scripting","title":"创建 JavaScript 代码块"},{"uri":"/zh-CN/docs/Learn_web_development/Core/Scripting/Functions","title":"函数——可复用的代码块"}],"popularity":null,"short_title":"函数——可复用的代码块","sidebarHTML":"<ol><li class=\"section\"><a href=\"/zh-CN/docs/Learn_web_development/Getting_started\">入门模块</a></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Environment_setup\">配置环境</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Environment_setup/Installing_software\">安装基础软件</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Environment_setup/Browsing_the_web\">网页、网站、网络服务器和搜索引擎的区别是什么？</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup/Code_editors\" class=\"only-in-en-us\">Code editors</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Environment_setup/Dealing_with_files\">处理文件</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Environment_setup/Command_line\">命令行速成课</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Your_first_website\">你的第一个网站</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Your_first_website/What_will_your_website_look_like\">你的网站会是什么样子？</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Your_first_website/Creating_the_content\">HTML 基础</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Your_first_website/Styling_the_content\">CSS 基础</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Your_first_website/Adding_interactivity\">JavaScript 基础</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Your_first_website/Publishing_your_website\">发布你的网站</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Getting_started/Web_standards\" class=\"only-in-en-us\">Web 标准</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Web_standards/How_the_web_works\">万维网是如何工作的</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Getting_started/Web_standards/The_web_standards_model\">Web 和 Web 标准</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Web_standards/How_browsers_load_websites\" class=\"only-in-en-us\">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\" class=\"only-in-en-us\">软性技能</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Research_and_learning\" class=\"only-in-en-us\">Research and learning</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Collaboration_and_teamwork\" class=\"only-in-en-us\">Collaboration and teamwork</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Workflows_and_processes\" class=\"only-in-en-us\">Workflows and processes</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Job_interviews\" class=\"only-in-en-us\">Succeeding in job interviews</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn_web_development/Core\" class=\"only-in-en-us\">核心模块</a></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content\">使用 HTML 构建内容</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Basic_HTML_syntax\">开始学习 HTML</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Webpage_metadata\">“头”里有什么——HTML 元信息</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Headings_and_paragraphs\">HTML 文本处理基础</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Emphasis_and_importance\">强调与重要性</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Lists\" class=\"only-in-en-us\">Lists</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Structuring_documents\">文档与网站架构</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Advanced_text_features\">文本格式进阶</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Creating_links\">创建超链接</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Marking_up_a_letter\">标记信件</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Structuring_a_page_of_content\">构建网页内容</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/HTML_images\">HTML 中的图片</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/HTML_video_and_audio\">视频和音频内容</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Mozilla_splash_page\">Mozilla 欢迎页面</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/HTML_table_basics\">HTML 表格基础</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Table_accessibility\">HTML 表格进阶特性和无障碍</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Planet_data_table\">作业：构建行星数据</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_forms\" class=\"only-in-en-us\">Forms and buttons in HTML</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Structuring_content/Debugging_HTML\">HTML 调试</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics\">CSS 样式基础</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/What_is_CSS\">CSS 如何运行</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Getting_started\">让我们开始 CSS 的学习之旅</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Styling_a_bio_page\">运用你的新知识</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Basic_selectors\">CSS 选择器</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Attribute_selectors\">属性选择器</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Pseudo_classes_and_elements\">伪类和伪元素</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Combinators\">关系选择器</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Box_model\">盒模型</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Handling_conflicts\">层叠、优先级与继承</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Values_and_units\">CSS 值和单位</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Sizing\">在 CSS 中调整大小</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Backgrounds_and_borders\">背景与边框</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Overflow\">溢出的内容</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Images_media_forms\">图像、媒体和表单元素</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Tables\">样式化表格</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Debugging_CSS\">调试 CSS</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Fundamental_CSS_comprehension\">基本的 CSS 理解</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Fancy_letterheaded_paper\">创建精美的信纸</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Styling_basics/Cool-looking_box\">一个漂亮的盒子</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Core/Text_styling\">CSS 文本样式</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Text_styling/Fundamentals\">基本文本和字体样式</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Text_styling/Styling_lists\">为列表添加样式</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Text_styling/Styling_links\">样式化链接</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Text_styling/Web_fonts\">Web 字体</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Text_styling/Typesetting_a_homepage\">作业：排版社区大学首页</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Core/CSS_layout\">CSS 排版</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Core/CSS_layout/Introduction\">介绍 CSS 布局</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/CSS_layout/Floats\">浮动</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/CSS_layout/Positioning\">定位</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/CSS_layout/Flexbox\">弹性盒子</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/CSS_layout/Grids\">网格</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/CSS_layout/Responsive_Design\">响应式设计</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/CSS_layout/Media_queries\">媒体查询入门指南</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/CSS_layout/Fundamental_Layout_Comprehension\">作业：基本布局理解</a></li></ol></details></li><li class=\"toggle\"><details open=\"\"><summary><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting\">使用 JavaScript 动态编码</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/What_is_JavaScript\">什么是 JavaScript？</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/A_first_splash\">JavaScript 初体验</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/What_went_wrong\">查找并解决 JavaScript 代码的错误</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Variables\">如何存储你需要的信息——变量</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Math\">JavaScript 中的基础数学 — 数字和操作符</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Strings\">文本处理——JavaScript 中的字符串</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Useful_string_methods\">有用的字符串方法</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Arrays\">数组</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Silly_story_generator\">笑话生成器</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Conditionals\">在代码中做决定——条件语句</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Loops\">循环吧，代码</a></li><li><em><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Functions\" aria-current=\"page\">函数——可复用的代码块</a></em></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Build_your_own_function\">创建你自己的函数</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Return_values\">函数返回值</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Events\">事件介绍</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Event_bubbling\">事件冒泡</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Image_gallery\">图片库</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Object_basics\">JavaScript 对象基础</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/DOM_scripting\">DOM 脚本简介</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Network_requests\">从服务器获取数据</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/JSON\">使用 JSON</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Scripting/Debugging_JavaScript\">处理常见的 JavaScript 问题</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Core/Frameworks_libraries\">JavaScript 架构和库</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Frameworks_libraries/Introduction\">客户端框架介绍</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Frameworks_libraries/Main_features\">框架的主要特性</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Frameworks_libraries/React_getting_started\">React 入门</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Frameworks_libraries/React_todo_list_beginning\">开始我们的 React 待办清单</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Frameworks_libraries/React_components\">组件化我们的 React App</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_events_state\" class=\"only-in-en-us\">React interactivity: Events and state</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_filtering_conditional_rendering\" class=\"only-in-en-us\">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_accessibility\" class=\"only-in-en-us\">Accessibility in React</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_resources\" class=\"only-in-en-us\">React resources</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Core/Accessibility\">无障碍</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Accessibility/What_is_accessibility\">什么是无障碍？</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Accessibility/Tooling\">解决常见的无障碍问题</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Accessibility/HTML\">HTML：无障碍的良好基础</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Accessibility/CSS_and_JavaScript\">CSS 和 JavaScript 无障碍最佳实践</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Accessibility/WAI-ARIA_basics\">WAI-ARIA 基础</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Accessibility/Multimedia\">多媒体无障碍</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Accessibility/Mobile\">移动端无障碍</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Accessibility/Accessibility_troubleshooting\">测验：无障碍疑难解答</a></li></ol></details></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Design_for_developers\" class=\"only-in-en-us\">为开发人员设计</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Core/Version_control\">版本控制</a></li><li class=\"section\"><a href=\"/en-US/docs/Learn_web_development/Extensions\" class=\"only-in-en-us\">扩展模块</a></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects\">Advanced JavaScript objects</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_prototypes\">对象原型</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object-oriented_programming\">面向对象编程基本概念</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Classes_in_JavaScript\">JavaScript 中的类</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_building_practice\">实践对象构造</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Adding_bouncing_balls_features\">为“弹球”示例添加新功能</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs\">客户端 Web API</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs/Introduction\">Web API 简介</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs/Video_and_audio_APIs\">视频和音频 API</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs/Drawing_graphics\">绘图</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs/Client-side_storage\">客户端存储</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Client-side_APIs/Third_party_APIs\">第三方 API</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Async_JS\">异步 JavaScript</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Async_JS/Introducing\">异步 JavaScript 简介</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Async_JS/Promises\">如何使用 Promise</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Async_JS/Implementing_a_promise-based_API\">如何实现基于 Promise 的 API</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Async_JS/Introducing_workers\">worker 简介</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Async_JS/Sequencing_animations\">序列动画</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Forms\">Web 表单</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Forms/Your_first_form\">创建我的第一个表单</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Forms/How_to_structure_a_web_form\">如何构建 HTML 表单</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Forms/Basic_native_form_controls\">原生表单部件</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Forms/HTML5_input_types\">HTML5 的输入（input）类型</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Forms/Other_form_controls\">其他表单控件</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Forms/Styling_web_forms\">样式化 Web 表单</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Forms/Advanced_form_styling\">表单样式化进阶</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Forms/UI_pseudo-classes\">UI 伪类</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Forms/Form_validation\">表单数据校验</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Forms/Sending_and_retrieving_form_data\">发送表单数据</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Client-side_tools\">理解客户端工具</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Client-side_tools/Overview\">客户端工具概述</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Client-side_tools/Package_management\">软件包管理基础</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Client-side_tools/Introducing_complete_toolchain\">介绍完整的工具链</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Client-side_tools/Deployment\">部署我们的应用</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side\">服务端网站</a></summary><ol><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/First_steps\">服务端基础</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/First_steps/Introduction\">服务端编程介绍</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/First_steps/Client-Server_overview\">客户端服务端交互概述</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/First_steps/Web_frameworks\">服务端 web 框架</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/First_steps/Website_security\">站点安全</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django\">Django web 框架（Python）</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Introduction\">Django 介绍</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/development_environment\">设置 Django 开发环境</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Tutorial_local_library_website\">Django Tutorial: The Local Library website</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/skeleton_website\">Django Tutorial Part 2: 创建网站的地基</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Models\">Django Tutorial Part 3: 使用模型</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Admin_site\">Django Tutorial Part 4: Django 管理员站点</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Home_page\">Django 教程 5：主页构建</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Generic_views\">Django 教程 6: 通用列表和详细信息视图</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Sessions\">Django 教程 7: 会话框架</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Authentication\">Django 教程 8：用户授权与许可</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Forms\">Django 教程 9: 使用表单</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Testing\">Django 教程 10: 测试 Django 网页应用</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/Deployment\">Django 教程 11：部署 Django 到生产环境</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/web_application_security\">Django Web 应用安全</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Django/django_assessment_blog\">评估：DIY Django 微博客</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs\">Express web 框架（Node.js）</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Introduction\">Express/Node 入门</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/development_environment\">设置 Node 开发环境</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Tutorial_local_library_website\">Express 教程：本地图书馆网站</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/skeleton_website\">Express 教程 2：创建站点框架</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/mongoose\">Express 教程 3：使用数据库 (Mongoose)</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/routes\">Express 教程 4：路由和控制器</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Displaying_data\">Express 教程 5: 呈现图书馆数据</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/forms\">Express 教程 6: 使用表单</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/deployment\">Express 教程 7：部署到生产环境</a></li></ol></details></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Performance\">Web 性能</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Performance/why_web_performance\">Web 性能的重要性</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Performance/What_is_web_performance\">什么是 web 性能？</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Performance/Perceived_performance\">感知性能</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Performance/Measuring_performance\">测量性能</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Performance/Multimedia\">多媒体：图片</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Performance/video\">多媒体：视频</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Performance/JavaScript\">JavaScript 性能优化</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Performance/HTML\">HTML 性能优化</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Performance/CSS\">CSS 性能优化</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Performance/business_case_for_performance\">web 性能的商业案例</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Testing\">测试</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Testing/Introduction\">跨浏览器测试介绍</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Testing/Testing_strategies\">测试的策略</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Testing/HTML_and_CSS\">处理常见的 HTML 和 CSS 问题</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Testing/Feature_detection\">实现特性检测</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Testing/Automated_testing\">自动化测试简介</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Extensions/Testing/Your_own_automation_environment\">搭建自己的自动化测试环境</a></li></ol></details></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Transform_animate\" class=\"only-in-en-us\">CSS 变换与动画化</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Security_privacy\" class=\"only-in-en-us\">安全与隐私</a></li><li class=\"section\">更多资源</li><li class=\"toggle\"><details><summary><a href=\"/zh-CN/docs/Learn_web_development/Howto\">如何解决常见问题</a></summary><ol><li><a href=\"/zh-CN/docs/Learn_web_development/Howto/Solve_HTML_problems\">使用 HTML 解决常见问题</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Howto/Solve_CSS_problems\">解决常见的 CSS 问题</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Howto/Solve_JavaScript_problems\">解决 JavaSctript 代码的常见问题</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Howto/Web_mechanics\">Web 机制</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Howto/Tools_and_setup\">工具和安装</a></li><li><a href=\"/zh-CN/docs/Learn_web_development/Howto/Design_and_accessibility\">设计与无障碍</a></li></ol></details></li><li><a href=\"/en-US/docs/Learn_web_development/About\" class=\"only-in-en-us\">关于</a></li><li><a href=\"/en-US/docs/Learn_web_development/Educators\" class=\"only-in-en-us\">面向教育工作者的资源</a></li><li><a href=\"/en-US/docs/Learn_web_development/Changelog\" class=\"only-in-en-us\">更新日志</a></li></ol>","source":{"folder":"zh-cn/learn_web_development/core/scripting/functions","github_url":"https://github.com/mdn/translated-content/blob/main/files/zh-cn/learn_web_development/core/scripting/functions/index.md","last_commit_url":"https://github.com/mdn/translated-content/commit/216c73b669a9760f7a444ebfbcb04a68bb3669d9","filename":"index.md"},"summary":"在 JavaScript 中另一个基本概念是函数, 它允许你在一个代码块中存储一段用于处理单任务的代码，然后在任何你需要的时候用一个简短的命令来调用，而不是把相同的代码写很多次。在本文中，我们将探索函数的基本概念，如函数的基本语法、如何定义和调用函数、函数的作用域和参数。","title":"函数——可复用的代码块","toc":[{"text":"我能在哪找到函数？","id":"我能在哪找到函数？"},{"text":"浏览器内置函数","id":"浏览器内置函数"},{"text":"函数与方法","id":"函数与方法"},{"text":"调用函数","id":"调用函数"},{"text":"函数参数","id":"函数参数"},{"text":"匿名函数和箭头函数","id":"匿名函数和箭头函数"},{"text":"函数作用域和冲突","id":"函数作用域和冲突"},{"text":"技能测试！","id":"技能测试！"},{"text":"总结","id":"总结"},{"text":"参见","id":"参见"}],"pageType":"learn-module-chapter"}}</script></body></html>