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- 2-8 整体配置结构
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- 2-9 多种配置类型
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- 3-8 使用 Angular2 框架
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- 3-9 为单页应用生成 HTML
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- 3-10 管理多个单页应用
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- 3-11 构建同构应用
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- 3-12 构建 Electron 应用
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- 3-13 构建 Npm 模块
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- 3-14 构建离线应用
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- 3-15 搭配 Npm Script
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- 3-16 检查代码
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- 3-17 通过 Node.js API 启动 Webpack
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- 3-18 使用 Webpack Dev Middleware
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- 3-19 加载图片
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- 3-20 加载SVG
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- 3-21 加载 Source Map
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- 3-22 实战总结
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- 第4章 优化
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- 4-1 缩小文件搜索范围
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- 4-2 使用 DllPlugin
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- 4-3 使用 HappyPack
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- 4-4 使用 ParallelUglifyPlugin
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- 4-5 使用自动刷新
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- 4-6 开启模块热替换
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- 4-7 区分环境
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- 4-8 压缩代码
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- 4-9 CDN 加速
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- 4-10 使用 Tree Shaking
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-
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- 5-1 工作原理概括
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- <h1 id="3-11-构建同构应用">3-11 构建同构应用</h1>
- <p>同构应用是指写一份代码但可同时在浏览器和服务器中运行的应用。</p>
- <h2 id="认识同构应用">认识同构应用</h2>
- <p>现在大多数单页应用的视图都是通过 JavaScript 代码在浏览器端渲染出来的,但在浏览器端渲染的坏处有:</p>
- <ul>
- <li>搜索引擎无法收录你的网页,因为展示出的数据都是在浏览器端异步渲染出来的,大部分爬虫无法获取到这些数据。</li>
- <li>对于复杂的单页应用,渲染过程计算量大,对低端移动设备来说可能会有性能问题,用户能明显感知到首屏的渲染延迟。</li>
- </ul>
- <p>为了解决以上问题,有人提出能否将原本只运行在浏览器中的 JavaScript 渲染代码也在服务器端运行,在服务器端渲染出带内容的 HTML 后再返回。
- 这样就能让搜索引擎爬虫直接抓取到带数据的 HTML,同时也能降低首屏渲染时间。
- 由于 Node.js 的流行和成熟,以及虚拟 DOM 提出与实现,使这个假设成为可能。</p>
- <p>实际上现在主流的前端框架都支持同构,包括 React、Vue2、Angular2,其中最先支持也是最成熟的同构方案是 React。
- 由于 React 使用者更多,它们之间又很相似,本节只介绍如何用 Webpack 构建 React 同构应用。</p>
- <p>同构应用运行原理的核心在于虚拟 DOM,虚拟 DOM 的意思是不直接操作 DOM 而是通过 JavaScript Object 去描述原本的 DOM 结构。
- 在需要更新 DOM 时不直接操作 DOM 树,而是通过更新 JavaScript Object 后再映射成 DOM 操作。</p>
- <p>虚拟 DOM 的优点在于:</p>
- <ul>
- <li>因为操作 DOM 树是高耗时的操作,尽量减少 DOM 树操作能优化网页性能。而 DOM Diff 算法能找出2个不同 Object 的最小差异,得出最小 DOM 操作;</li>
- <li>虚拟 DOM 的在渲染的时候不仅仅可以通过操作 DOM 树来表示出结果,也能有其它的表示方式,例如把虚拟 DOM 渲染成字符串(服务器端渲染),或者渲染成手机 App 原生的 UI 组件( React Native)。</li>
- </ul>
- <p>以 React 为例,核心模块 <code>react</code> 负责管理 React 组件的生命周期,而具体的渲染工作可以交给 <code>react-dom</code> 模块来负责。</p>
- <p><code>react-dom</code> 在渲染虚拟 DOM 树时有2中方式可选:</p>
- <ul>
- <li>通过 <code>render()</code> 函数去操作浏览器 DOM 树来展示出结果。</li>
- <li>通过 <code>renderToString()</code> 计算出表示虚拟 DOM 的 HTML 形式的字符串。</li>
- </ul>
- <p>构建同构应用的最终目的是从一份项目源码中构建出2份 JavaScript 代码,一份用于在浏览器端运行,一份用于在 Node.js 环境中运行渲染出 HTML。
- 其中用于在 Node.js 环境中运行的 JavaScript 代码需要注意以下几点:</p>
- <ul>
- <li>不能包含浏览器环境提供的 API,例如使用 <code>document</code> 进行 DOM 操作,  因为 Node.js 不支持这些 API;</li>
- <li>不能包含 CSS 代码,因为服务端渲染的目的是渲染出 HTML 内容,渲染出 CSS 代码会增加额外的计算量,影响服务端渲染性能;</li>
- <li>不能像用于浏览器环境的输出代码那样把 <code>node_modules</code> 里的第三方模块和 Node.js 原生模块(例如 <code>fs</code> 模块)打包进去,而是需要通过 CommonJS 规范去引入这些模块。</li>
- <li>需要通过 CommonJS 规范导出一个渲染函数,以用于在 HTTP 服务器中去执行这个渲染函数,渲染出 HTML 内容返回。</li>
- </ul>
- <h2 id="解决方案">解决方案</h2>
- <p>接下来改造在<a href="3-6使用React框架.html">3-6使用 React 框架</a>中介绍的 React 项目,为它增加构建同构应用的功能。</p>
- <p>由于要从一份源码构建出2份不同的代码,需要有2份 Webpack 配置文件分别与之对应。
- 构建用于浏览器环境的配置和前面讲的没有差别,本节侧重于讲如何构建用于服务端渲染的代码。</p>
- <p>用于构建浏览器环境代码的 <code>webpack.config.js</code> 配置文件保留不变,新建一个专门用于构建服务端渲染代码的配置文件 <code>webpack_server.config.js</code>,内容如下:</p>
- <pre><code class="lang-js"><span class="hljs-keyword">const</span> path = <span class="hljs-built_in">require</span>(<span class="hljs-string">'path'</span>);
- <span class="hljs-keyword">const</span> nodeExternals = <span class="hljs-built_in">require</span>(<span class="hljs-string">'webpack-node-externals'</span>);
- <span class="hljs-built_in">module</span>.exports = {
- <span class="hljs-comment">// JS 执行入口文件</span>
- entry: <span class="hljs-string">'./main_server.js'</span>,
- <span class="hljs-comment">// 为了不把 Node.js 内置的模块打包进输出文件中,例如 fs net 模块等</span>
- target: <span class="hljs-string">'node'</span>,
- <span class="hljs-comment">// 为了不把 node_modules 目录下的第三方模块打包进输出文件中</span>
- externals: [nodeExternals()],
- output: {
- <span class="hljs-comment">// 为了以 CommonJS2 规范导出渲染函数,以给采用 Node.js 编写的 HTTP 服务调用</span>
- libraryTarget: <span class="hljs-string">'commonjs2'</span>,
- <span class="hljs-comment">// 把最终可在 Node.js 中运行的代码输出到一个 bundle_server.js 文件</span>
- filename: <span class="hljs-string">'bundle_server.js'</span>,
- <span class="hljs-comment">// 输出文件都放到 dist 目录下</span>
- path: path.resolve(__dirname, <span class="hljs-string">'./dist'</span>),
- },
- <span class="hljs-built_in">module</span>: {
- rules: [
- {
- test: <span class="hljs-regexp">/\.js$/</span>,
- use: [<span class="hljs-string">'babel-loader'</span>],
- exclude: path.resolve(__dirname, <span class="hljs-string">'node_modules'</span>),
- },
- {
- <span class="hljs-comment">// CSS 代码不能被打包进用于服务端的代码中去,忽略掉 CSS 文件</span>
- test: <span class="hljs-regexp">/\.css$/</span>,
- use: [<span class="hljs-string">'ignore-loader'</span>],
- },
- ]
- },
- devtool: <span class="hljs-string">'source-map'</span> <span class="hljs-comment">// 输出 source-map 方便直接调试 ES6 源码</span>
- };
- </code></pre>
- <p>以上代码有几个关键的地方,分别是:</p>
- <ul>
- <li><code>target: 'node'</code> 由于输出代码的运行环境是 Node.js,源码中依赖的 Node.js 原生模块没必要打包进去;</li>
- <li><code>externals: [nodeExternals()]</code> <a href="https://github.com/liady/webpack-node-externals" target="_blank">webpack-node-externals</a> 的目的是为了防止 node_modules 目录下的第三方模块被打包进去,因为 Node.js 默认会去 node_modules 目录下寻找和使用第三方模块;</li>
- <li><code>{test: /\.css$/, use: ['ignore-loader']}</code> 忽略掉依赖的 CSS 文件,CSS 会影响服务端渲染性能,又是做服务端渲不重要的部分;</li>
- <li><code>libraryTarget: 'commonjs2'</code> 以 CommonJS2 规范导出渲染函数,以供给采用 Node.js 编写的 HTTP 服务器代码调用。</li>
- </ul>
- <p>为了最大限度的复用代码,需要调整下目录结构:</p>
- <p>把页面的根组件放到一个单独的文件 <code>AppComponent.js</code>,该文件只能包含根组件的代码,不能包含渲染入口的代码,而且需要导出根组件以供给渲染入口调用,<code>AppComponent.js</code> 内容如下:</p>
- <pre><code class="lang-jsx"><span class="hljs-keyword">import</span> React, { Component } <span class="hljs-keyword">from</span> <span class="hljs-string">'react'</span>;
- <span class="hljs-keyword">import</span> <span class="hljs-string">'./main.css'</span>;
- <span class="hljs-keyword">export</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">AppComponent</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">Component</span> </span>{
- render() {
- <span class="hljs-keyword">return</span> <span class="xml"><span class="hljs-tag"><<span class="hljs-name">h1</span>></span>Hello,Webpack<span class="hljs-tag"></<span class="hljs-name">h1</span>></span></span>
- }
- }
- </code></pre>
- <p>分别为不同环境的渲染入口写两份不同的文件,分别是用于浏览器端渲染 DOM 的 <code>main_browser.js</code> 文件,和用于服务端渲染 HTML 字符串的 <code>main_server.js</code> 文件。</p>
- <p><code>main_browser.js</code> 文件内容如下:</p>
- <pre><code class="lang-js"><span class="hljs-keyword">import</span> React <span class="hljs-keyword">from</span> <span class="hljs-string">'react'</span>;
- <span class="hljs-keyword">import</span> { render } <span class="hljs-keyword">from</span> <span class="hljs-string">'react-dom'</span>;
- <span class="hljs-keyword">import</span> { AppComponent } <span class="hljs-keyword">from</span> <span class="hljs-string">'./AppComponent'</span>;
- <span class="hljs-comment">// 把根组件渲染到 DOM 树上</span>
- render(<span class="xml"><span class="hljs-tag"><<span class="hljs-name">AppComponent</span>/></span></span>, <span class="hljs-built_in">window</span>.document.getElementById(<span class="hljs-string">'app'</span>));
- </code></pre>
- <p><code>main_server.js</code> 文件内容如下:</p>
- <pre><code class="lang-js"><span class="hljs-keyword">import</span> React <span class="hljs-keyword">from</span> <span class="hljs-string">'react'</span>;
- <span class="hljs-keyword">import</span> { renderToString } <span class="hljs-keyword">from</span> <span class="hljs-string">'react-dom/server'</span>;
- <span class="hljs-keyword">import</span> { AppComponent } <span class="hljs-keyword">from</span> <span class="hljs-string">'./AppComponent'</span>;
- <span class="hljs-comment">// 导出渲染函数,以给采用 Node.js 编写的 HTTP 服务器代码调用</span>
- <span class="hljs-keyword">export</span> <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">render</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-comment">// 把根组件渲染成 HTML 字符串</span>
- <span class="hljs-keyword">return</span> renderToString(<span class="xml"><span class="hljs-tag"><<span class="hljs-name">AppComponent</span>/></span></span>)
- }
- </code></pre>
- <p>为了能把渲染的完整 HTML 文件通过 HTTP 服务返回给请求端,还需要通过用 Node.js 编写一个 HTTP 服务器。
- 由于本节不专注于将 HTTP 服务器的实现,就采用了 ExpressJS 来实现,<code>http_server.js</code> 文件内容如下:</p>
- <pre><code class="lang-js"><span class="hljs-keyword">const</span> express = <span class="hljs-built_in">require</span>(<span class="hljs-string">'express'</span>);
- <span class="hljs-keyword">const</span> { render } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'./dist/bundle_server'</span>);
- <span class="hljs-keyword">const</span> app = express();
- <span class="hljs-comment">// 调用构建出的 bundle_server.js 中暴露出的渲染函数,再拼接下 HTML 模版,形成完整的 HTML 文件</span>
- app.get(<span class="hljs-string">'/'</span>, <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params">req, res</span>) </span>{
- res.send(<span class="hljs-string">`
- <html>
- <head>
- <meta charset="UTF-8">
- </head>
- <body>
- <div id="app"><span class="hljs-subst">${render()}</span></div>
- <!--导入 Webpack 输出的用于浏览器端渲染的 JS 文件-->
- <script src="./dist/bundle_browser.js"></script>
- </body>
- </html>
- `</span>);
- });
- <span class="hljs-comment">// 其它请求路径返回对应的本地文件</span>
- app.use(express.static(<span class="hljs-string">'.'</span>));
- app.listen(<span class="hljs-number">3000</span>, <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-built_in">console</span>.log(<span class="hljs-string">'app listening on port 3000!'</span>)
- });
- </code></pre>
- <p>再安装新引入的第三方依赖:</p>
- <pre><code class="lang-bash"><span class="hljs-comment"># 安装 Webpack 构建依赖</span>
- npm i -D css-loader style-loader ignore-loader webpack-node-externals
- <span class="hljs-comment"># 安装 HTTP 服务器依赖</span>
- npm i -S express
- </code></pre>
- <p>以上所有准备工作已经完成,接下来执行构建,编译出目标文件:</p>
- <ul>
- <li>执行命令 <code>webpack --config webpack_server.config.js</code> 构建出用于服务端渲染的 <code>./dist/bundle_server.js</code> 文件。</li>
- <li>执行命令 <code>webpack</code> 构建出用于浏览器环境运行的 <code>./dist/bundle_browser.js</code> 文件,默认的配置文件为 <code>webpack.config.js</code>。</li>
- </ul>
- <p>构建执行完成后,执行 <code>node ./http_server.js</code> 启动 HTTP 服务器后,再用浏览器去访问 <code>http://localhost:3000</code> 就能看到 <code>Hello,Webpack</code> 了。
- 但是为了验证服务端渲染的结果,你需要打开浏览器的开发工具中的网络抓包一栏,再重新刷新浏览器后,就能抓到请求 HTML 的包了,抓包效果图如下:</p>
- <p><img src="img/3-11server-render.png" alt="图3.9.1 服务端渲染抓包"></p>
- <p>可以看到服务器返回的是渲染出内容后的 HTML 而不是 HTML 模版,这说明同构应用的改造完成。</p>
- <blockquote>
- <p>本实例<a href="http://webpack.wuhaolin.cn/3-11构建同构应用.zip" target="_blank">提供项目完整代码</a></p>
- </blockquote>
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