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class="text" data-v-6646d2d3>JavaScript基础</p><!--]--><!----></a><div class="caret" role="button" data-v-6646d2d3><!----></div></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-6646d2d3 data-v-6646d2d3><div class="item" data-v-6646d2d3><div class="indicator" data-v-6646d2d3></div><a class="VPLink link link" href="/note/CSS.html" data-v-6646d2d3 data-v-857b9044><!--[--><p class="text" data-v-6646d2d3>CSS基础</p><!--]--><!----></a><div class="caret" role="button" data-v-6646d2d3><!----></div></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-6646d2d3 data-v-6646d2d3><div class="item" data-v-6646d2d3><div class="indicator" data-v-6646d2d3></div><a class="VPLink link link" href="/note/JavaScriptEnhanced.html" data-v-6646d2d3 data-v-857b9044><!--[--><p class="text" data-v-6646d2d3>JavaScript进阶</p><!--]--><!----></a><div class="caret" role="button" data-v-6646d2d3><!----></div></div><!----></div><div class="VPSidebarItem level-1 is-link is-active has-active" data-v-6646d2d3 data-v-6646d2d3><div class="item" data-v-6646d2d3><div class="indicator" data-v-6646d2d3></div><a class="VPLink link link" href="/note/Front-end%20Engineering.html" data-v-6646d2d3 data-v-857b9044><!--[--><p class="text" data-v-6646d2d3>前端工程化</p><!--]--><!----></a><div class="caret" role="button" data-v-6646d2d3><!----></div></div><!----></div><!--]--></div></section></div><!--]--><!--[--><!--]--></nav></aside><div class="VPContent has-sidebar" id="VPContent" data-v-23299678 data-v-f76a1d95><div class="VPDoc has-sidebar has-aside" data-v-f76a1d95 data-v-e32ad3fb><div class="container" data-v-e32ad3fb><div class="aside" data-v-e32ad3fb><div class="aside-curtain" data-v-e32ad3fb></div><div class="aside-container" data-v-e32ad3fb><div class="aside-content" data-v-e32ad3fb><div class="VPDocAside" data-v-e32ad3fb data-v-1b364ca7><!--[--><!--]--><!--[--><!--]--><div class="VPDocAsideOutline" data-v-1b364ca7 data-v-ac019323><div class="content" data-v-ac019323><div class="outline-marker" data-v-ac019323></div><div class="outline-title" data-v-ac019323>On this page</div><nav aria-labelledby="doc-outline-aria-label" data-v-ac019323><span class="visually-hidden" id="doc-outline-aria-label" data-v-ac019323> Table of Contents for current page </span><ul class="root" data-v-ac019323 data-v-e23b97f7><!--[--><!--]--></ul></nav></div></div><!--[--><!--]--><div class="spacer" data-v-1b364ca7></div><!--[--><!--]--><!----><!--[--><!--]--><!--[--><!--]--></div></div></div></div><div class="content" data-v-e32ad3fb><div class="content-container" data-v-e32ad3fb><!--[--><!--]--><main class="main" data-v-e32ad3fb><div style="position:relative;" class="vp-doc _note_Front-end%20Engineering" data-v-e32ad3fb><div><h1 id="前端工程化" tabindex="-1">前端工程化 <a class="header-anchor" href="#前端工程化" aria-hidden="true">#</a></h1><h2 id="node-js" tabindex="-1">Node.js <a class="header-anchor" href="#node-js" aria-hidden="true">#</a></h2><ul><li>什么是Node.JS Node的应用场景</li><li>JS代码执行</li><li>Node的输入和输出</li><li>Node的全局对象</li></ul><h3 id="什么是node-js" tabindex="-1">什么是Node.js <a class="header-anchor" href="#什么是node-js" aria-hidden="true">#</a></h3><p>Node.js是一个基于<strong>V8 JavaScript引擎</strong>的<strong>JavaScript运行时环境</strong></p><ul><li>V8可以嵌入到任何C++应用程序中，无论是Chrome还是Node.js，事实上都嵌入了V8引擎来执行JavaScript代码</li><li>在Chrome浏览器中，还需要解析、渲染HTML、CSS等相关渲染引擎，另外还需要支持浏览器操作的API、浏览器自己的事件循环</li><li>在Node.js中我们也需要进行一些额外操作：文件系统读写、网络IO、加密、压缩解压文件等</li></ul><p>可以简单总结出Node.js和浏览器的区别</p><ul><li><p>Chrome浏览器</p><ul><li><p>Blink负责解析HTML文档，遇到JavaScript标签时将内容交给V8引擎</p></li><li><blockquote><p>Blink 是 Google Chrome 浏览器的渲染引擎，V8 是 Blink 内置的 JavaScript 引擎</p></blockquote><ul><li>预分析：检查语法错误但不生成AST树</li><li>生成AST：语法分析、词法分析后，生成抽象语法树（AST） <ul><li>AST 为每一行代码定义键值对。初始类型标识符定义 AST 属于一个程序，然后所有代码行将定义在主体内部，主体是一个对象数组。</li></ul></li><li>生成字节码：基线编译器（Ignition）将 AST 转换为字节码</li><li>生成机器代码：优化编译器 (Turbofan) 将字节码转换为优化的机器代码。另外，在逐行执行字节码的过程中，<strong>如果一段代码经常被执行，V8会直接将这段代码转换并保存为机器码</strong>，下次执行不需要经过字节码，优化了执行速度</li></ul></li></ul></li><li><p>Node.js</p><ul><li>只处理JavaScript代码 内部V8引擎负责JS代码的执行</li><li>JavaScript代码 -&gt; V8 -&gt; Node.js Bindings -&gt; LibUV</li><li>LibUV是使用<strong>C语言编写的库</strong>，提供了<strong>事件循环、文件系统读写、网络IO、线程池</strong>等等内容</li></ul></li></ul><p>![The Node.js System](Front-end Engineering.assets/The Node.js System.jpeg)</p><h3 id="node-js的应用场景" tabindex="-1">Node.js的应用场景 <a class="header-anchor" href="#node-js的应用场景" aria-hidden="true">#</a></h3><ul><li>前端开发的库都是以node包形式管理的</li><li>npm yarn pnpm成为前端开发使用最多的工具</li><li>使用Node.js作为Web服务器开发、中间件、代理服务器</li><li>借助Node.js完成前后端渲染的同构应用</li><li>编写脚本工具 构建项目 打包代码等</li><li>Electron桌面应用程序</li></ul><h3 id="node-js的参数传递" tabindex="-1">Node.js的参数传递 <a class="header-anchor" href="#node-js的参数传递" aria-hidden="true">#</a></h3><h4 id="process-argv" tabindex="-1"><code>process.argv</code> <a class="header-anchor" href="#process-argv" aria-hidden="true">#</a></h4><p><code>process.argv</code>返回一个数组</p><ul><li>在代码中通过<code>process.argv[2]</code>读取来自命令行的额外参数</li><li><code>process.argv[0]</code> <code>process.argv[1]</code>分别为<code>node.exe</code>的绝对路径和<code>目标文件</code>的绝对路径</li></ul><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// sum.js</span></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> x </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> process</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">argv[</span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">]</span></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> y </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> process</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">argv[</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">]</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(x </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> y)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><div class="language-sh line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;"># 通过命令行运行node执行脚本 并传入参数</span></span>
<span class="line"><span style="color:#FFCB6B;">node</span><span style="color:#A6ACCD;"> </span><span style="color:#C3E88D;">sum.js</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">5</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">10</span><span style="color:#A6ACCD;"> </span><span style="color:#676E95;font-style:italic;"># 15</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h4 id="console" tabindex="-1">console <a class="header-anchor" href="#console" aria-hidden="true">#</a></h4><ul><li><code>console.log</code> 打印内容到stdout并加上换行符</li><li><code>console.clear</code> 清空当前stdout中的内容</li><li><code>console.trace</code> 打印字符串<code>Trace: </code>到stderr <ul><li>将堆栈跟踪打印到代码中的当前位置</li></ul></li></ul><h4 id="repl" tabindex="-1">REPL <a class="header-anchor" href="#repl" aria-hidden="true">#</a></h4><p>在浏览器的控制台选项卡中，我们可以通过输入JS代码与之交互，在Node.js中同样提供了类似的功能</p><ul><li>REPL是Read-Eval-Print Loop的简称，翻译为：读取-求值-输出循环</li><li>REPL是一个<strong>简单的、交互式的编程环境</strong></li><li>在命令行窗口中输入<code>node</code>即可进入</li></ul><h3 id="node中的全局对象" tabindex="-1">Node中的全局对象 <a class="header-anchor" href="#node中的全局对象" aria-hidden="true">#</a></h3><p>在浏览器中，我们可以在JS代码中访问全局对象<code>window</code>，代表当前标签窗口</p><p>在Node.js中的全局对象名为<code>global</code>，在控制台输出<code>global</code>对象：</p><div class="language-sh line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;"> global</span></span>
<span class="line"><span style="color:#89DDFF;">&lt;</span><span style="color:#A6ACCD;">ref </span><span style="color:#89DDFF;">*</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;"> Object </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">global</span><span style="color:#89DDFF;">]</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">global:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Circular </span><span style="color:#89DDFF;">*</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">]</span><span style="color:#A6ACCD;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">clearInterval:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Function: clearInterval</span><span style="color:#89DDFF;">]</span><span style="color:#A6ACCD;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">clearTimeout:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Function: clearTimeout</span><span style="color:#89DDFF;">]</span><span style="color:#A6ACCD;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">setInterval:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Function: setInterval</span><span style="color:#89DDFF;">]</span><span style="color:#A6ACCD;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">setTimeout:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Function: setTimeout</span><span style="color:#89DDFF;">]</span><span style="color:#A6ACCD;"> </span><span style="color:#C3E88D;">{</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Symbol(nodejs.util.promisify.custom)</span><span style="color:#89DDFF;">]</span><span style="color:#82AAFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Getter</span><span style="color:#89DDFF;">]</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">}</span><span style="color:#A6ACCD;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">queueMicrotask:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Function: queueMicrotask</span><span style="color:#89DDFF;">]</span><span style="color:#A6ACCD;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">performance:</span><span style="color:#A6ACCD;"> </span><span style="color:#C3E88D;">Performance</span><span style="color:#A6ACCD;"> </span><span style="color:#C3E88D;">{</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">nodeTiming:</span><span style="color:#A6ACCD;"> </span><span style="color:#C3E88D;">PerformanceNodeTiming</span><span style="color:#A6ACCD;"> </span><span style="color:#C3E88D;">{</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">name:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">node</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">entryType:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">node</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">startTime:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">0</span><span style="color:#C3E88D;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">duration:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2245.9675999991596</span><span style="color:#C3E88D;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">nodeStart:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1.7120999991893768</span><span style="color:#C3E88D;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">v8Start:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">7.749699998646975</span><span style="color:#C3E88D;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">bootstrapComplete:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">56.47019999846816</span><span style="color:#C3E88D;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">environment:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">28.44789999909699</span><span style="color:#C3E88D;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">loopStart:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">97.62589999847114</span><span style="color:#C3E88D;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">loopExit:</span><span style="color:#A6ACCD;"> </span><span style="color:#C3E88D;">-1,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">idleTime:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2070.0206</span></span>
<span class="line"><span style="color:#A6ACCD;"> },</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">timeOrigin:</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1675854922619.539</span></span>
<span class="line"><span style="color:#A6ACCD;"> },</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">clearImmediate:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Function: clearImmediate</span><span style="color:#89DDFF;">]</span><span style="color:#A6ACCD;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">setImmediate:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Function: setImmediate</span><span style="color:#89DDFF;">]</span><span style="color:#A6ACCD;"> </span><span style="color:#C3E88D;">{</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Symbol(nodejs.util.promisify.custom)</span><span style="color:#89DDFF;">]</span><span style="color:#82AAFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#A6ACCD;">Getter</span><span style="color:#89DDFF;">]</span></span>
<span class="line"><span style="color:#A6ACCD;"> }</span></span>
<span class="line"><span style="color:#A6ACCD;">}</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br></div></div><h4 id="常见的全局对象" tabindex="-1">常见的全局对象 <a class="header-anchor" href="#常见的全局对象" aria-hidden="true">#</a></h4><ul><li><code>Buffer</code></li><li><code>clearImmediate</code></li><li><code>clearInterval</code></li><li><code>clearTimeout</code></li><li><code>console</code><ul><li>和控制台交互</li></ul></li><li><code>process</code><ul><li>提供了Node进程中相关的信息</li><li>Node的运行环境、系统环境变量、参数等</li></ul></li><li><code>queueMicrotask(callback)</code></li><li><code>setImmediate(callback, [, ...args])</code></li><li><code>setInterval(callback, delay[, ...args])</code></li><li><code>setTimeout(callback, delay[, ...args])</code></li><li><code>TextDecoder</code></li><li><code>TextEncoder</code></li><li><code>URL</code></li><li><code>URLSearchParams</code></li><li><code>WebAssembly</code></li></ul><h4 id="特殊的全局对象" tabindex="-1">特殊的全局对象 <a class="header-anchor" href="#特殊的全局对象" aria-hidden="true">#</a></h4><p><code>__dirname</code> <code>__filename</code> <code>exports</code> <code>module</code> <code>require()</code></p><ul><li>这些变量看起来是全局的，其实并不是（它们仅存在于模块范围内），只是每个模块中都有</li><li>它们在命令行交互中是不可使用的</li><li><code>__dirname</code> 当前模块的目录名</li><li><code>__filename</code> 当前模块的文件名</li><li><code>exports</code> <code>module</code> <code>require()</code>将在模块章节中讲解</li></ul><h4 id="global对象" tabindex="-1"><code>global</code>对象 <a class="header-anchor" href="#global对象" aria-hidden="true">#</a></h4><p><code>global</code>是一个全局对象</p><ul><li>在Node.js环境下，之前的 <code>process</code> <code>console</code> <code>setTimeout</code>等都有被放入到<code>global</code>中</li><li>而在浏览器中，这些全局API是被放到<code>window</code>对象上的</li></ul><p>这无异于增加了开发者的心智负担，所以在最新的ECMA标准中出现了<code>globalThis</code>，指向全局对象</p><ul><li>在浏览器中的<code>globalThis</code>指向<code>window</code>对象</li><li>在Node.js中的<code>globalThis</code>指向<code>global</code>对象</li></ul><p>两个全局对象的区别：在浏览器中通过<code>var</code>定义的变量会被放到<code>window</code>对象上，而Node.js不会</p><h2 id="模块化开发" tabindex="-1">模块化开发 <a class="header-anchor" href="#模块化开发" aria-hidden="true">#</a></h2><ul><li>认识模块化开发</li><li>CommonJS和Node</li><li>require函数解析</li><li>AMD和CMD（已经被时代淘汰 了解即可）</li><li>ESModule用法详解</li><li>ESModule运行原理</li></ul><h3 id="模块化的初衷" tabindex="-1">模块化的初衷 <a class="header-anchor" href="#模块化的初衷" aria-hidden="true">#</a></h3><ul><li>将大的程序拆分成一个个小的易于维护的代码</li><li>每个模块负责程序中的一部分逻辑，拥有<strong>自己的作用域</strong>、<strong>定义变量名时不会发生冲突</strong></li><li>模块可以暴露<strong>变量、函数、对象</strong>等导出</li><li>模块可以导入其他模块的<strong>变量、函数、对象</strong></li></ul><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// moduleA.js</span></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> moduleA </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> (</span><span style="color:#C792EA;">function</span><span style="color:#89DDFF;">(){</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#C792EA;">const</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">name</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">Ziu</span><span style="color:#89DDFF;">&quot;</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#C792EA;">const</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">age</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#F78C6C;">18</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#C792EA;">const</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">run</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">()</span><span style="color:#F07178;"> </span><span style="color:#C792EA;">=&gt;</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#F07178;">(</span><span style="color:#A6ACCD;">name</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">+</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">age</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">+</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">is running.</span><span style="color:#89DDFF;">&#39;</span><span style="color:#F07178;">)</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#89DDFF;font-style:italic;">return</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">name</span><span style="color:#89DDFF;">,</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">age</span><span style="color:#89DDFF;">,</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">run</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#89DDFF;">}</span><span style="color:#A6ACCD;">)()</span></span>
<span class="line"></span>
<span class="line"><span style="color:#676E95;font-style:italic;">// moduleB.js</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(moduleA</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">name) </span><span style="color:#676E95;font-style:italic;">// 在其他模块中调用</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br></div></div><h3 id="commonjs" tabindex="-1">CommonJS <a class="header-anchor" href="#commonjs" aria-hidden="true">#</a></h3><p>CommonJS是一种<strong>规范</strong>，当初命名为ServerJS，旨在浏览器以外的地方使用，后为体现其广泛性，改名为CommonJS，简称CJS</p><p><strong>规范 是用来指导 实现的</strong></p><ul><li><code>Node</code> 是CommonJS在服务端的代表<strong>实现</strong></li><li><code>Browserify</code> 是CommonJS在浏览器中的一种<strong>实现</strong> （正在被淘汰）</li><li><code>WebPack</code> 打包工具具备支持CommonJS的支持和转换</li></ul><p>所以，Node.js对CommonJS进行了支持和实现，让JavaScript在Node上运行时可以实现模块化开发</p><ul><li>每个<code>.js</code>文件都是一个单独的模块</li><li>每个模块中都包含变量<code>exports</code> <code>module.exports</code> <code>require</code></li></ul><div class="vp-code-group"><div class="tabs"><input type="radio" name="group-CBSdq" id="tab-pTRDqQu" checked="checked"><label for="tab-pTRDqQu">env.js</label><input type="radio" name="group-CBSdq" id="tab-fmDIdBz"><label for="tab-fmDIdBz">utils.js</label><input type="radio" name="group-CBSdq" id="tab-eOcz8lc"><label for="tab-eOcz8lc">index.js</label></div><div class="blocks"><div class="language-js active line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// env.js</span></span>
<span class="line"><span style="color:#89DDFF;">exports.</span><span style="color:#A6ACCD;">name </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Ziu</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"><span style="color:#89DDFF;">exports.</span><span style="color:#A6ACCD;">age </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">18</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// utils.js</span></span>
<span class="line"><span style="color:#89DDFF;">module.exports</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">sum</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">function</span><span style="color:#89DDFF;">(</span><span style="color:#A6ACCD;font-style:italic;">x</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#A6ACCD;font-style:italic;">y</span><span style="color:#89DDFF;">)</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#89DDFF;font-style:italic;">return</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">x</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">+</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">y</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// index.js</span></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> utils </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">require</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">utils.js</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"><span style="color:#A6ACCD;">utils</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">sum</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span><span style="color:#A6ACCD;"> sum </span><span style="color:#89DDFF;">}</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">require</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">utils.js</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"><span style="color:#82AAFF;">sum</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span><span style="color:#A6ACCD;"> name</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> age </span><span style="color:#89DDFF;">}</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">require</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">env.js</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(name</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> age) </span><span style="color:#676E95;font-style:italic;">// Ziu 18</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div></div></div><h4 id="exports的本质" tabindex="-1"><code>exports</code>的本质 <a class="header-anchor" href="#exports的本质" aria-hidden="true">#</a></h4><p><code>exports</code>和<code>require</code>在Node中的本质</p><ul><li><code>exports</code>是一个对象，我们可以在这个对象中添加很多属性，添加的属性则会被导出 <ul><li>在没有向该对象添加任何属性之前，它是一个空对象</li></ul></li><li>当通过<code>require</code>导入时：<code>const env = require(&#39;env.js&#39;)</code><ul><li><code>env</code>这个变量等于<code>env.js</code>中的<code>exports</code>对象</li><li>本质上是<code>env</code>是<code>exports</code>对象的引用赋值</li></ul></li></ul><div class="vp-code-group"><div class="tabs"><input type="radio" name="group-qlwKH" id="tab-BJsRSn6" checked="checked"><label for="tab-BJsRSn6">utils.js</label><input type="radio" name="group-qlwKH" id="tab-QNhrcGS"><label for="tab-QNhrcGS">index.js</label></div><div class="blocks"><div class="language-js active line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// utils.js</span></span>
<span class="line"><span style="color:#89DDFF;">exports.</span><span style="color:#A6ACCD;">a </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">0</span></span>
<span class="line"></span>
<span class="line"><span style="color:#676E95;font-style:italic;">// 1s后修改a值</span></span>
<span class="line"><span style="color:#82AAFF;">setTimeout</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">=&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#89DDFF;">exports.</span><span style="color:#A6ACCD;">a</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#F78C6C;">1</span></span>
<span class="line"><span style="color:#89DDFF;">},</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1000</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span>
<span class="line"><span style="color:#676E95;font-style:italic;">// 2s后检查a值</span></span>
<span class="line"><span style="color:#82AAFF;">setTimeout</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">=&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#F07178;">(</span><span style="color:#89DDFF;">exports.</span><span style="color:#A6ACCD;">a</span><span style="color:#F07178;">) </span><span style="color:#676E95;font-style:italic;">// 2</span></span>
<span class="line"><span style="color:#89DDFF;">},</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2000</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// index.js</span></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> utils </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">require</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">./utils</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(utils</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">a) </span><span style="color:#676E95;font-style:italic;">// 0</span></span>
<span class="line"></span>
<span class="line"><span style="color:#82AAFF;">setTimeout</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">=&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#F07178;">(</span><span style="color:#A6ACCD;">utils</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">a</span><span style="color:#F07178;">) </span><span style="color:#676E95;font-style:italic;">// 1</span></span>
<span class="line"><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">utils</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">a</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#F78C6C;">2</span><span style="color:#F07178;"> </span><span style="color:#676E95;font-style:italic;">// 反过来修改a值</span></span>
<span class="line"><span style="color:#89DDFF;">},</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1500</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div></div></div><p>在上述代码中，<code>utils</code>对象中的属性<code>a</code>在一秒后被赋值为<code>1</code>，因此在index.js中输出<code>utils.a</code>得到了两次不同的结果</p><p>反过来，在index.js中修改导入的<code>utils.a</code>的值后，修改结果也会反映在<code>exports.a</code>上，输出的值为<code>2</code></p><p>实际开发中不要修改导入模块中的变量，改变原模块中变量的值并不规范</p><h4 id="module-exports" tabindex="-1"><code>module.exports</code> <a class="header-anchor" href="#module-exports" aria-hidden="true">#</a></h4><p>在Node.js中，真正常用的导出方式是<code>module.exports</code></p><ul><li><code>module.exports</code>本质上就是<code>exports</code>对象（同一个内存地址）</li><li>可以直接给<code>exports</code>对象赋值，将需要导出的内容统一导出</li><li>给<code>module.exports</code>重新赋值，即改变了<code>exports</code>对象的指向，<strong>后续的修改不再影响原模块中的变量</strong></li></ul><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> name </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Ziu</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> run </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">=&gt;</span><span style="color:#A6ACCD;"> console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(name </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">is running.</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span>
<span class="line"><span style="color:#89DDFF;">module.exports</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;"> name</span><span style="color:#89DDFF;">,</span></span>
<span class="line"><span style="color:#A6ACCD;"> run</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><h4 id="二者的区别" tabindex="-1">二者的区别 <a class="header-anchor" href="#二者的区别" aria-hidden="true">#</a></h4><p>既然如此，为什么还要存在<code>exports</code>这个概念呢？</p><ul><li>在CommonJS中是没有<code>module.exports</code>的概念的</li><li>为了实现模块的导出，Node.js使用的是<code>Module</code>类，每一个模块都是<code>Module</code>的实例，也就是<code>module</code></li><li>所以在Node.js中真正用于导出的并不是<code>exports</code>，而是<code>module.exports</code></li><li><code>module</code>对象中的<code>exports</code>属性是<code>exports</code>对象的一个引用 <ul><li><code>module.exports === exports === utils</code></li></ul></li></ul><p>如果<code>module.exports</code>不再引用<code>exports</code>对象了，修改<code>exports</code>对象也就没有意义了</p><div class="vp-code-group"><div class="tabs"><input type="radio" name="group-3p0G9" id="tab-CNXya7o" checked="checked"><label for="tab-CNXya7o">utils.js</label><input type="radio" name="group-3p0G9" id="tab-F3F9LQi"><label for="tab-F3F9LQi">index.js</label></div><div class="blocks"><div class="language-js active line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// utils.js</span></span>
<span class="line"><span style="color:#89DDFF;">module.exports</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;"> </span><span style="color:#F07178;">name</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Ziu</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#89DDFF;">exports.</span><span style="color:#A6ACCD;">age </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">18</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><div class="language-js line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">js</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#676E95;font-style:italic;">// index.js</span></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> utils </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">require</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">utils.js</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(utils</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">name) </span><span style="color:#676E95;font-style:italic;">// Ziu</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(utils</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">age) </span><span style="color:#676E95;font-style:italic;">// undefined</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div></div></div><p>当使用<code>module.exports = { ... }</code>后，模块中原有的<code>exports</code>不再被导入识别，导入的内容将变为<code>module.exports</code>指定的对象内容</p><h4 id="require的本质" tabindex="-1"><code>require</code>的本质 <a class="header-anchor" href="#require的本质" aria-hidden="true">#</a></h4><p><code>require</code>是一个函数，可以帮助我们导入一个文件（模块）中导出的对象</p><ul><li>为什么可以省略掉<code>.js</code>后缀，直接使用<code>require(&#39;./utils&#39;)</code></li><li>为什么可以省略掉<code>index.js</code>，直接使用<code>require(&#39;./tools&#39;)</code>导入<code>tools/index.js</code></li></ul><p>这涉及到<code>require</code>在匹配路径后的查找规则：</p><p>分为三种情况：<strong>内置模块、自定义路径、包名</strong></p><ul><li>导入Node.js内置的模块，如<code>const path = require(&#39;path&#39;)</code><ul><li>直接返回该内置模块 并停止后续的查找</li></ul></li><li>根据路径导入自定义的模块，如<code>const utils = require(&#39;./{filename}&#39;)</code><ul><li>按照路径寻找该模块<code>./</code> <code>../</code> <code>/</code></li><li>如果指定了后缀名，则按照后缀名查找</li><li>如果未指定后缀名，则： <ol><li>直接查找该文件</li><li>查找<code>{filename}.js</code>文件</li><li>查找<code>{filename}.json</code>文件</li><li>查找<code>{filename}.node</code>文件</li></ol></li><li>如果按照上述方式没找到文件，则<strong>将<code>{filename}</code>作为路径继续查找</strong></li><li>查找目录下的<code>index</code>文件 <code>{filename}/index</code><ol><li>查找<code>{filename}/index.js</code>文件</li><li>··· ···</li></ol></li><li>没找到：报错<code>Cannot find module &#39;xxx&#39;</code></li></ul></li><li>包名，如<code>const lodash = require(&#39;lodash&#39;)</code><ul><li>到项目根目录的<code>node_modules</code>中查找</li><li><code>node_modules/{package_name}/index.js</code></li><li>当前项目目录的<code>node_modules</code>找不到则继续向上查找，直到查找到根目录的<code>node_modules</code></li></ul></li></ul><h4 id="模块的加载过程" tabindex="-1">模块的加载过程 <a class="header-anchor" href="#模块的加载过程" aria-hidden="true">#</a></h4><ul><li>模块在被第一次引入时，模块中的JS代码会被运行一次 <ul><li>代码执行顺序与<code>require</code>的位置相关</li></ul></li><li>模块如果被多次引入，会被缓存，最终只加载一次 <ul><li>这是因为每个模块对象<code>module</code>上都有一个属性<code>loaded</code></li><li><code>loaded === false</code>表示该模块尚未被加载</li><li>第二次被<code>require</code>引入时会检查该属性是否为<code>true</code></li></ul></li><li>如果有循环引用，加载顺序如何？ <ul><li>数据结构：图结构（graph）遍历时有深度优先搜索（DFS）、广度优先搜索（BFS）两种算法</li><li>Node采用的是深度优先算法</li></ul></li></ul><h4 id="commonjs的缺点" tabindex="-1">CommonJS的缺点 <a class="header-anchor" href="#commonjs的缺点" aria-hidden="true">#</a></h4><ul><li>加载模块是同步加载的 <ul><li>只有等到对应的模块加载完毕，当前模块中的内容才能被执行</li><li>当然，在服务器中加载JS文件都是本地文件，加载速度非常快，不会受影响</li></ul></li><li>但是在浏览器中使用CommonJS <ul><li>需要先从服务器下载JS文件，后加载运行</li><li>阻塞JS执行 阻塞页面加载</li></ul></li><li>在WebPack中使用CommonJS <ul><li>CommonJS会被WebPack解析</li><li>将CommonJS代码转化为bundle 浏览器可以直接运行</li></ul></li></ul></div></div></main><!--[--><!--]--><footer class="VPDocFooter" data-v-e32ad3fb data-v-26128c3c><div class="edit-info" data-v-26128c3c><div class="edit-link" data-v-26128c3c><a class="VPLink link edit-link-button" href="https://github.com/ZiuChen/ZiuChen.github.io/edit/main/docs/note/Front-end Engineering.md" target="_blank" rel="noreferrer" data-v-26128c3c data-v-857b9044><!--[--><svg xmlns="http://www.w3.org/2000/svg" viewbox="0 0 24 24" class="edit-link-icon" data-v-26128c3c><path d="M18,23H4c-1.7,0-3-1.3-3-3V6c0-1.7,1.3-3,3-3h7c0.6,0,1,0.4,1,1s-0.4,1-1,1H4C3.4,5,3,5.4,3,6v14c0,0.6,0.4,1,1,1h14c0.6,0,1-0.4,1-1v-7c0-0.6,0.4-1,1-1s1,0.4,1,1v7C21,21.7,19.7,23,18,23z"></path><path d="M8,17c-0.3,0-0.5-0.1-0.7-0.3C7,16.5,6.9,16.1,7,15.8l1-4c0-0.2,0.1-0.3,0.3-0.5l9.5-9.5c1.2-1.2,3.2-1.2,4.4,0c1.2,1.2,1.2,3.2,0,4.4l-9.5,9.5c-0.1,0.1-0.3,0.2-0.5,0.3l-4,1C8.2,17,8.1,17,8,17zM9.9,12.5l-0.5,2.1l2.1-0.5l9.3-9.3c0.4-0.4,0.4-1.1,0-1.6c-0.4-0.4-1.2-0.4-1.6,0l0,0L9.9,12.5z M18.5,2.5L18.5,2.5L18.5,2.5z"></path></svg> Edit this page on GitHub<!--]--><!----></a></div><div class="last-updated" data-v-26128c3c><p class="VPLastUpdated" data-v-26128c3c data-v-a6a422eb>Updated Date: <time datetime="2023-02-08T15:10:40.000Z" data-v-a6a422eb></time></p></div></div><div class="prev-next" data-v-26128c3c><div class="pager" data-v-26128c3c><a class="pager-link prev" href="/note/JavaScriptEnhanced.html" data-v-26128c3c><span class="desc" data-v-26128c3c>Previous page</span><span class="title" data-v-26128c3c>JavaScript进阶</span></a></div><div class="has-prev pager" data-v-26128c3c><!----></div></div></footer><!--[--><!--]--></div></div></div></div></div><footer class="VPFooter has-sidebar" data-v-23299678 data-v-bfc7af0b><div class="container" data-v-bfc7af0b><p class="message" data-v-bfc7af0b>Released under the MIT License.</p><p class="copyright" data-v-bfc7af0b>Copyright © 2019-present Ziu Chen</p></div></footer><!--[--><!--]--></div></div>
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