Angular Universal：服务端渲染link

Angular Universal: server-side renderinglink

本指南讲的是Angular Universal（统一平台），一项在服务端运行 Angular 应用的技术。

This guide describes Angular Universal, a technology that runs your Angular application on the server.

标准的 Angular 应用会运行在浏览器中，它会在 DOM 中渲染页面，以响应用户的操作。

A normal Angular application executes in the browser, rendering pages in the DOM in response to user actions.

而Angular Universal 会在服务端通过一个名叫服务端渲染（server-side rendering - SSR）的过程生成静态的应用页面。

Angular Universal generates static application pages on the server through a process called server-side rendering (SSR).

它可以生成这些页面，并在浏览器请求时直接用它们给出响应。 也可以把页面预先生成为 HTML 文件，然后把它们作为静态文件供服务器使用。

When Universal is integrated with your app, it can generate and serve those pages in response to requests from browsers. It can also pre-generate pages as HTML files that you serve later.

你可以使用 Angular CLI 来轻松为应用做好服务端渲染的准备。CLI 的 @nguniversal/express-engine 模板会执行下面所讲的必要步骤。

You can easily prepare an app for server-side rendering using the Angular CLI. The CLI schematic @nguniversal/express-engine performs the required steps, as described below.

本指南讲的是一个 Universal 的范例应用，它启动得和在服务端渲染好的页面一样快。 稍后，浏览器就会下载完整的客户端版本，并在代码加载完之后自动切换过去。

This guide describes a Universal sample application that launches quickly as a server-rendered page. Meanwhile, the browser downloads the full client version and switches to it automatically after the code loads.

为何需要服务端渲染？link

Why use server-side rendering?link

有三个主要的理由来为你的应用创建一个 Universal 版本。

There are three main reasons to create a Universal version of your app.

1. 帮助网络爬虫（SEO）

   Facilitate web crawlers (SEO)

2. 提升在手机和低功耗设备上的性能

   Improve performance on mobile and low-powered devices

3. 迅速显示出第一个页面

   Show the first page quickly

帮助网络爬虫link

Facilitate web crawlerslink

Google、Bing、Facebook、Twitter 和其它社交媒体网站都依赖网络爬虫去索引你的应用内容，并且让它的内容可以通过网络搜索到。

Google, Bing, Facebook, Twitter, and other social media sites rely on web crawlers to index your application content and make that content searchable on the web.

这些网络爬虫可能不会像人类那样导航到你的具有高度交互性的 Angular 应用，并为其建立索引。

These web crawlers may be unable to navigate and index your highly interactive Angular application as a human user could do.

Angular Universal 可以为你生成应用的静态版本，它易搜索、可链接，浏览时也不必借助 JavaScript。 它也让站点可以被预览，因为每个 URL 返回的都是一个完全渲染好的页面。

Angular Universal can generate a static version of your app that is easily searchable, linkable, and navigable without JavaScript. Universal also makes a site preview available since each URL returns a fully rendered page.

启用对网络爬虫的支持通常也称作搜索引擎优化 (SEO)。

Enabling web crawlers is often referred to as search engine optimization (SEO).

提升手机和低功耗设备上的性能link

Improve performance on mobile and low-powered deviceslink

有些设备不支持 JavaScript 或 JavaScript 执行得很差，导致用户体验不可接受。 对于这些情况，你可能会需要该应用的服务端渲染的、无 JavaScript 的版本。 虽然有一些限制，不过这个版本可能是那些完全没办法使用该应用的人的唯一选择。

Some devices don't support JavaScript or execute JavaScript so poorly that the user experience is unacceptable. For these cases, you may require a server-rendered, no-JavaScript version of the app. This version, however limited, may be the only practical alternative for people who otherwise couldn't use the app at all.

快速显示第一页link

Show the first page quicklylink

快速显示第一页对于吸引用户是至关重要的。

Displaying the first page quickly can be critical for user engagement.

如果页面加载超过了三秒钟，那么 53% 的移动网站会被放弃。 你的应用要启动得更快一点，以便在用户决定做别的事情之前吸引他们的注意力。

53percent of mobile site visits are abandoned if pages take longer than 3 seconds to load. Your app may have to launch faster to engage these users before they decide to do something else.

使用 Angular Universal，你可以为应用生成“着陆页”，它们看起来就和完整的应用一样。 这些着陆页是纯 HTML，并且即使 JavaScript 被禁用了也能显示。 这些页面不会处理浏览器事件，不过它们可以用 [routerLink](guide/router#router-link) 在这个网站中导航。

With Angular Universal, you can generate landing pages for the app that look like the complete app. The pages are pure HTML, and can display even if JavaScript is disabled. The pages don't handle browser events, but they do support navigation through the site using routerLink.

在实践中，你可能要使用一个着陆页的静态版本来保持用户的注意力。 同时，你也会在幕后加载完整的 Angular 应用。 用户会觉得着陆页几乎是立即出现的，而当完整的应用加载完之后，又可以获得完整的交互体验。

In practice, you'll serve a static version of the landing page to hold the user's attention. At the same time, you'll load the full Angular app behind it. The user perceives near-instant performance from the landing page and gets the full interactive experience after the full app loads.

Universal Web 服务器link

Universal web serverslink

Universal Web 服务器使用 Universal 模板引擎渲染出的静态 HTML 来响应对应用页面的请求。 服务器接收并响应来自客户端（通常是浏览器）的 HTTP 请求，并回复静态文件，如脚本、CSS 和图片。 它可以直接响应数据请求，也可以作为独立数据服务器的代理进行响应。

A Universal web server responds to application page requests with static HTML rendered by the Universal template engine. The server receives and responds to HTTP requests from clients (usually browsers), and serves static assets such as scripts, CSS, and images. It may respond to data requests, either directly or as a proxy to a separate data server.

这个例子中的范例 Web 服务器是基于常见的 Express 框架的。

The sample web server for this guide is based on the popular Express framework.

要制作一个 Universal 应用，就要安装 platform-server 包，它提供了 DOM 的服务端实现、XMLHttpRequest 以及其它不依赖浏览器的底层特性。 使用 platform-server 模块（代替 platform-browser 模块）编译客户端应用，并在 Web 服务器上运行其生成的 Universal 应用。

To make a Universal app, install the platform-server package, which provides server implementations of the DOM, XMLHttpRequest, and other low-level features that don't rely on a browser. Compile the client application with the platform-server module (instead of the platform-browser module) and run the resulting Universal app on a web server.

服务器（这个例子中使用的是 Node Express 服务器）会把客户端对应用页面的请求传给 renderModuleFactory() 函数。

The server (Node Express in this guide's example) passes client requests for application pages to Universal's renderModuleFactory() function.

renderModuleFactory() 函数接受一个模板 HTML 页面（通常是 index.html）、一个包含组件的 Angular 模块和一个用于决定该显示哪些组件的路由作为输入。

The renderModuleFactory() function takes as inputs a template HTML page (usually index.html), an Angular module containing components, and a route that determines which components to display.

该路由从客户端的请求中传给服务器。

The route comes from the client's request to the server.

每次请求都会给出所请求路由的一个适当的视图。

Each request results in the appropriate view for the requested route.

renderModuleFactory() 在模板中的 <app> 标记中渲染出这个视图，并为客户端创建一个完成的 HTML 页面。

The renderModuleFactory() function renders the view within the <app> tag of the template, creating a finished HTML page for the client.

最后，服务器就会把渲染好的页面返回给客户端。

Finally, the server returns the rendered page to the client.

准备服务端渲染link

Preparing for server-side renderinglink

要想让应用可以在服务器上渲染，就要对应用自身做一些修改，然后搭建服务器环境。

Before your app can be rendered on a server, you must make changes in the app itself, and also set up the server.

1. 安装依赖。

   Install dependencies.

2. 通过修改应用代码及其配置进行准备。

   Prepare your app by modifying both the app code and its configuration.

3. 添加构建目标，并使用 CLI 中的 @nguniversal/express-engine 原理图来构建出 Universal 包。

   Add a build target, and build a Universal bundle using the CLI with the @nguniversal/express-engine schematic.

4. 设置服务器，以运行 Universal 包。

   Set up a server to run Universal bundles.

5. 打包并在服务器上运行此应用。

   Pack and run the app on the server.

下面各节将会更详细的介绍这些主要步骤。

The following sections go into each of these main steps in more detail.

步骤一：安装依赖link

Step 1: Install dependencieslink

把 @angular/platform-server 安装到项目中。在项目中使用与其它 @angular 包相同的版本。你还需要 ts-loader 供 Webpack 构建时使用，还要安装 @nguniversal/module-map-ngfactory-loader 来处理服务端渲染环境下的惰性加载。

Install @angular/platform-server into your project. Use the same version as the other @angular packages in your project. You also need ts-loader for your webpack build and @nguniversal/module-map-ngfactory-loader to handle lazy-loading in the context of a server-render.

      
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      $ npm install --save @angular/platform-server @nguniversal/module-map-ngfactory-loader ts-loader
    

步骤二：准备你的应用link

Step 2: Prepare your applink

要让你的应用为 Universal 渲染做好准备，要遵循如下步骤：

To prepare your app for Universal rendering, take the following steps:

• 为应用添加 Universal 支持。

  Add Universal support to your app.

• 创建服务端根模块。

  Create a server root module.

• 创建一个 main 文件，以导出服务端根模块。

  Create a main file to export the server root module.

• 配置服务端根模块。

  Configure the server root module.

2a. 为应用添加 Universal 支持link

2a. Add Universal support to your applink

要想让你的 AppModule 与 Universal 兼容，就要在 src/app/app.module.ts 中导入时 BrowserModule 添加一个 .withServerTransition() 并带上应用的 ID。

Make your AppModule compatible with Universal by adding .withServerTransition() and an application ID to your BrowserModule import in src/app/app.module.ts.

      
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      @NgModule({
  bootstrap: [AppComponent],
  imports: [
    // Add .withServerTransition() to support Universal rendering.
    // The application ID can be any identifier which is unique on
    // the page.
    BrowserModule.withServerTransition({appId: 'my-app'}),
    ...
  ],

})
export class AppModule {}
    

2b. 创建服务端根模块link

2b. Create a server root modulelink

在服务器上运行时，要创建一个名叫 AppServerModule 的模块作为根模块。这个例子中把它放在了 app.module.ts 附近的 app.server.module.ts 文件中。这个新模块从 AppModule 中导入了所有东西，并且导入了 ServerModule。它还添加了 ModuleMapLoaderModule 以便在通过 Angular CLI 进行服务端渲染时也能使用惰性加载路由。

Create a module named AppServerModule to act as the root module when running on the server. This example places it alongside app.module.ts in a file named app.server.module.ts. The new module imports everything from the root AppModule, and adds ServerModule. It also adds ModuleMapLoaderModule to help make lazy-loaded routes possible during server-side renders with the Angular CLI.

下面是 src/app/app.server.module.ts 的例子。

Here's an example in src/app/app.server.module.ts.

      
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      import {NgModule} from '@angular/core';
import {ServerModule} from '@angular/platform-server';
import {ModuleMapLoaderModule} from '@nguniversal/module-map-ngfactory-loader';

import {AppModule} from './app.module';
import {AppComponent} from './app.component';

@NgModule({
  imports: [
    // The AppServerModule should import your AppModule followed
    // by the ServerModule from @angular/platform-server.
    AppModule,
    ServerModule,
    ModuleMapLoaderModule // <-- *Important* to have lazy-loaded routes work
  ],
  // Since the bootstrapped component is not inherited from your
  // imported AppModule, it needs to be repeated here.
  bootstrap: [AppComponent],
})
export class AppServerModule {}
    

2c. 创建一个 main 文件，导出 AppServerModulelink

2c. Create a main file to export AppServerModulelink

在应用的 src/ 目录下为你的 Universal 包创建一个 main 文件，以导出 AppServerModule 实例。在这个例子里它叫 main.server.ts。

Create a main file for your Universal bundle in the app src/ folder to export your AppServerModule instance. This example calls the file main.server.ts.

      
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      export { AppServerModule } from './app/app.server.module';
    

2d. 为 AppServerModule 创建配置文件link

2d. Create a configuration file for AppServerModulelink

把 tsconfig.app.json 复制到 tsconfig.server.json 中，并做如下修改：

Copy tsconfig.app.json to tsconfig.server.json and modify it as follows:

• 在 "compilerOptions" 中，把 "module" 改为 "commonjs"。

  In "compilerOptions", set the "module" target to "commonjs".

• 添加一个 "angularCompilerOptions" 节，并把 "entryModule"（入口模块）指向你的 AppServerModule 实例，格式为 importPath#symbolName。在这个例子中，这个入口模块是 app/app.server.module#AppServerModule。

  Add a section for "angularCompilerOptions" and set "entryModule" to point to your AppServerModule instance. Use the format importPath#symbolName. In this example, the entry module is app/app.server.module#AppServerModule.

      
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      {
  "extends": "../tsconfig.json",
  "compilerOptions": {
    "outDir": "../out-tsc/app",
    "baseUrl": "./",
    // Set the module format to "commonjs":
    "module": "commonjs",
    "types": []
  },
  "exclude": [
    "test.ts",
    "**/*.spec.ts"
  ],
  // Add "angularCompilerOptions" with the AppServerModule you wrote
  // set as the "entryModule".
  "angularCompilerOptions": {
    "entryModule": "app/app.server.module#AppServerModule"
  }
}
    

步骤三：创建新的构建目标，并打包link

Step 3: Create a new build target and build the bundlelink

打开本项目的 Angular 配置文件 angular.json，并在 "architect" 节下添加一个新的目标。下面的例子中把这个新目标命名为 "server"。

Open the Angular configuration file, angular.json, for your project, and add a new target in the "architect" section for the server build. The following example names the new target "server".

      
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      "architect": {
  "build": { ... }
  "server": {
    "builder": "@angular-devkit/build-angular:server",
    "options": {
      "outputPath": "dist/my-project-server",
      "main": "src/main.server.ts",
      "tsConfig": "src/tsconfig.server.json"
    }
  }
}
    

要想为应用程序构建服务包，请使用 ng run 命令，格式为 projectName#serverTarget。在这个例子中，目前已配置了两个目标 "build" 和 "server"。

To build a server bundle for your application, use the ng run command, with the format projectName#serverTarget. In our example, there are now two targets configured, "build" and "server".

      
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      # This builds your project using the server target, and places the output
# in dist/my-project-server/
$ ng run my-project:server

Date: 2017-07-24T22:42:09.739Z
Hash: 9cac7d8e9434007fd8da
Time: 4933ms
chunk {0} main.js (main) 9.49 kB [entry] [rendered]
chunk {1} styles.css (styles) 0 bytes [entry] [rendered]
    

步骤四：设置服务器环境，以运行 Universal 包link

Step 4: Set up a server to run Universal bundleslink

要想运行 Universal 包，你需要把它发送给服务器。

To run a Universal bundle, you need to send it to a server.

下面的例子中把 AppServerModule（用 AOT 编译的）传给了 PlatformServer 的 renderModuleFactory()，它会序列化该应用，并把结果返回给浏览器。

The following example passes AppServerModule (compiled with AoT) to the PlatformServer method renderModuleFactory(), which serializes the app and returns the result to the browser.

      
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      app.engine('html', (_, options, callback) => {
  renderModuleFactory(AppServerModuleNgFactory, {
    // Our index.html
    document: template,
    url: options.req.url,
    // configure DI to make lazy-loading work differently
    // (we need to instantly render the view)
    extraProviders: [
      provideModuleMap(LAZY_MODULE_MAP)
    ]
  }).then(html => {
    callback(null, html);
  });
});
    

该技术为你提供了完全的灵活性。方便起见，你还可以使用具有一些内置功能的 @nguniversal/express-engine 工具。

This technique gives you complete flexibility. For convenience, you can also use the @nguniversal/express-engine tool that has some built-in features.

      
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      import { ngExpressEngine } from '@nguniversal/express-engine';

app.engine('html', ngExpressEngine({
  bootstrap: AppServerModuleNgFactory,
  providers: [
    provideModuleMap(LAZY_MODULE_MAP)
  ]
}));
    

下面的简单例子实现了一个骨架级 Node Express 服务器来解决这些问题。 （注意，它只能用于演示，在实际生产环境中，你还要设置身份验证和安全性。）

The following simple example implements a bare-bones Node Express server to fire everything up. (Note that this is for demonstration only. In a real production environment, you need to set up additional authentication and security.)

在应用的根目录下，紧挨着 package.json，创建一个名叫 server.ts 的文件，并添加如下内容。

At the root level of your project, next to package.json, create a file named server.ts and add the following content.

      
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      // These are important and needed before anything else
import 'zone.js/dist/zone-node';
import 'reflect-metadata';

import { renderModuleFactory } from '@angular/platform-server';
import { enableProdMode } from '@angular/core';

import * as express from 'express';
import { join } from 'path';
import { readFileSync } from 'fs';

// Faster server renders w/ Prod mode (dev mode never needed)
enableProdMode();

// Express server
const app = express();

const PORT = process.env.PORT || 4000;
const DIST_FOLDER = join(process.cwd(), 'dist');

// Our index.html we'll use as our template
const template = readFileSync(join(DIST_FOLDER, 'browser', 'index.html')).toString();

// * NOTE :: leave this as require() since this file is built Dynamically from webpack
const { AppServerModuleNgFactory, LAZY_MODULE_MAP } = require('./dist/server/main.bundle');

const { provideModuleMap } = require('@nguniversal/module-map-ngfactory-loader');

app.engine('html', (_, options, callback) => {
  renderModuleFactory(AppServerModuleNgFactory, {
    // Our index.html
    document: template,
    url: options.req.url,
    // DI so that we can get lazy-loading to work differently (since we need it to just instantly render it)
    extraProviders: [
      provideModuleMap(LAZY_MODULE_MAP)
    ]
  }).then(html => {
    callback(null, html);
  });
});

app.set('view engine', 'html');
app.set('views', join(DIST_FOLDER, 'browser'));

// Server static files from /browser
app.get('*.*', express.static(join(DIST_FOLDER, 'browser')));

// All regular routes use the Universal engine
app.get('*', (req, res) => {
  res.render(join(DIST_FOLDER, 'browser', 'index.html'), { req });
});

// Start up the Node server
app.listen(PORT, () => {
  console.log(`Node server listening on http://localhost:${PORT}`);
});
    

步骤五：打包并在服务器上运行此应用link

Step 5: Pack and run the app on the serverlink

设置 webpack 配置，以处理 Node Express 的 server.ts 文件，并启动应用服务器。

Set up a webpack configuration to handle the Node Express server.ts file and serve your application.

在应用的根目录下，创建一个 Webpack 配置文件 webpack.server.config.js，它会把 server.ts 及其依赖编译到 dist/server.js 中。

In your app root directory, create a webpack configuration file (webpack.server.config.js) that compiles the server.ts file and its dependencies into dist/server.js.

      
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      const path = require('path');
const webpack = require('webpack');

module.exports = {
  entry: {  server: './server.ts' },
  resolve: { extensions: ['.js', '.ts'] },
  target: 'node',
  // this makes sure we include node_modules and other 3rd party libraries
  externals: [/(node_modules|main\..*\.js)/],
  output: {
    path: path.join(__dirname, 'dist'),
    filename: '[name].js'
  },
  module: {
    rules: [
      { test: /\.ts$/, loader: 'ts-loader' }
    ]
  },
  plugins: [
    // Temporary Fix for issue: https://github.com/angular/angular/issues/11580
    // for "WARNING Critical dependency: the request of a dependency is an expression"
    new webpack.ContextReplacementPlugin(
      /(.+)?angular(\\|\/)core(.+)?/,
      path.join(__dirname, 'src'), // location of your src
      {} // a map of your routes
    ),
    new webpack.ContextReplacementPlugin(
      /(.+)?express(\\|\/)(.+)?/,
      path.join(__dirname, 'src'),
      {}
    )
  ]
}
    

项目的 dist/ 目录现在同时包含 browser 目录和 server 目录。

The project's dist/ folder now contains both browser and server folders.

      
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      dist/
   browser/
   server/
    

要想在服务器上运行该应用，请在命令行窗口运行下列命令：

To run the app on the server, type the following in a command shell.

      
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      node dist/server.js
    

创建一些脚本link

Creating scriptslink

现在，来创建一些便利脚本，在以后帮助我们完成这些琐事。 你可以在 Angular 配置文件 angular.json 的 "server" 区添加这些脚本。

Now let's create a few handy scripts to help us do all of this in the future. You can add these in the "server" section of the Angular configuration file, angular.json.

      
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      "architect": {
  "build": { ... }
  "server": {
    ...
     "scripts": {
      // Common scripts
      "build:ssr": "npm run build:client-and-server-bundles && npm run webpack:server",
      "serve:ssr": "node dist/server.js",

      // Helpers for the scripts
      "build:client-and-server-bundles": "ng build --prod && ng build --prod --app 1 --output-hashing=false",
      "webpack:server": "webpack --config webpack.server.config.js --progress --colors"
    }
   ...
    

要想在本地系统上使用 Universal 运行应用的生产版本，请使用如下命令：

To run a production build of your app with Universal on your local system, use the following command.

      
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      npm run build:ssr && npm run serve:ssr
    

使用浏览器 APIlink

Working around the browser APIslink

由于 Universal 的 platform-server 应用并没有运行在浏览器中，因此你不得不在该服务器中缺少某些浏览器 API 和能力的情况下工作。

Because a Universal platform-server app doesn't execute in the browser, you may have to work around some of the browser APIs and capabilities that are missing on the server.

比如，你的服务端渲染页面不能引用浏览器独有的原生对象，比如 window、document、navigator 或 location。 如果你在服务端渲染的页面中不需要它们，就可以使用条件逻辑跳过它们。 另一种方式是查找一个可注入的 Angular 对所需对象的抽象服务，比如 Location 或 Document，它可能作为你调用的指定 API 的等价替身。 如果 Angular 没有提供它，你也可以写一个自己的抽象层，当在浏览器中运行时，就把它委托给浏览器 API，当它在服务器中运行时，就提供一个符合要求的代用实现。

For example, your server-side page can't reference browser-only native objects such as window, document, navigator, or location. If you don't need these on the server-rendered page, you can side-step them with conditional logic. Alternatively, you can find an injectable Angular abstraction over the object you need such as Location or Document; it may substitute adequately for the specific API that you're calling. If Angular doesn't provide it, you can write your own abstraction that delegates to the browser API while in the browser and to a satisfactory alternative implementation while on the server.

同样，由于没有鼠标或键盘事件，因此 Universal 应用也不能依赖于用户点击某个按钮来显示每个组件。 Universal 应用必须仅仅根据客户端过来的请求决定要渲染的内容。 把该应用做成可路由的，就是一种好方案。

Similarly, without mouse or keyboard events, a server-side app can't rely on a user clicking a button to show a component. The app must determine what to render based solely on the incoming client request. This is a good argument for making the app routable.

由于服务端渲染页面的用户只能点击链接，所以你应该尽快让它切换到真正的客户端应用，以提供正常的交互体验。

Because the user of a server-rendered page can't do much more than click links, you should swap in the real client app as quickly as possible for a proper interactive experience.

例子link

Universal tutoriallink

《英雄指南》教程是本章所讲的 Universal 范例的基础。

The Tour of Heroes tutorial is the foundation for this walkthrough.

除了下面讲的少量修改之外，应用中的核心文件几乎不用动。 你只需要添加一些额外的文件来支持使用 Universal 进行构建和提供服务。

The core application files are mostly untouched, with a few exceptions described below. You'll add more files to support building and serving with Universal.

在这个例子中，Angular CLI 会使用 AOT (预先) 编译器对该应用的 Universal 版本进行编译和打包。 Node.js® 的 Express Web 服务器会把客户端请求转换成由 Universal 渲染出的页面。

In this example, the Angular CLI compiles and bundles the Universal version of the app with the Ahead-of-Time (AoT) compiler. A Node Express web server turns client requests into the HTML pages rendered by Universal.

要想创建服务端渲染模块 app.server.module.ts，请运行下列 CLI 命令。

To create server-side app module, app.server.module.ts, run the following CLI command.

      
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      ng add @nguniversal/express-engine --clientProject angular.io-example
    

该命令会创建如下的目录结构。

The command creates the following folder structure.

      
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      src/
  index.html                 应用的宿主页app web page
  main.ts                    客户端应用的引导程序bootstrapper for client app
  main.server.ts             * 服务端应用的引导程序* bootstrapper for server app
  tsconfig.app.json          TypeScript 的客户端配置TypeScript client configuration
  tsconfig.server.json       * TypeScript 的服务端配置* TypeScript server configuration
  tsconfig.spec.json         TypeScript 的测试配置TypeScript spec configuration
  style.css                  应用的样式表styles for the app
  app/ ...                   应用代码application code
    app.server.module.ts     * 服务端的应用模块* server-side application module
server.ts                    * Express 的服务程序* express web server
tsconfig.json                TypeScript 的客户端配置TypeScript client configuration
package.json                 npm 配置npm configuration
webpack.server.config.js     * Webpack 的服务端配置* webpack server configuration
    

那些标有 * 的文件都是新的，而不是来自原来的范例应用。 本文稍后的部分会涉及它们。

The files marked with * are new and not in the original tutorial sample. This guide covers them in the sections below.

在 HTTP 中使用绝对地址link

Using absolute URLs for server requestslink

教程中的 HeroService 和 HeroSearchService 都委托了 Angular 的 HttpClient 模块来获取应用数据。 那些服务都把请求发送到了相对 URL，比如 api/heroes。

The tutorial's HeroService and HeroSearchService delegate to the Angular HttpClient module to fetch application data. These services send requests to relative URLs such as api/heroes.

在 Universal 应用中，HTTP 的 URL 必须是绝对地址（比如 https://my-server.com/api/heroes）， 只有这样，Universal 的 Web 服务器才能处理那些请求。 这意味着当运行在服务端时，你要修改你的服务，来使用绝对 URL发起请求，而在浏览器中，则使用相对 URL。

In a Universal app, HTTP URLs must be absolute(for example, https://my-server.com/api/heroes) even when the Universal web server is capable of handling relative requests. This means you need to change your services to make requests with absolute URLs when running on the server and with relative URLs when running in the browser.

解决方案之一是通过 Angular 的 APP_BASE_HREF 令牌来提供服务器的源地址（origin），把它注入到服务中，并把这个源地址添加到所请求的 URL 之前。

One solution is to provide the server's runtime origin under Angular's APP_BASE_HREFtoken, inject it into the service, and prepend the origin to the request URL.

先为 HeroService 的构造函数添加第二个参数 origin，它是可选的，并通过 APP_BASE_HREF 令牌进行注入。

Start by changing the HeroService constructor to take a second origin parameter that is optionally injected via the APP_BASE_HREF token.

      
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      constructor(
  private http: HttpClient,
  private messageService: MessageService,
  @Optional() @Inject(APP_BASE_HREF) origin: string) {
    this.heroesUrl = `${origin}${this.heroesUrl}`;
  }
    

这个构造函数使用了 @Optional() 指令来为 heroesUrl 添加源（如果有的话）。

The constructor uses the @Optional() directive to prepend the origin to heroesUrl if it exists.

在浏览器版本中，你不用提供 APP_BASE_HREF，因此 heroesUrl 仍然是相对的。

You don't provide APP_BASE_HREF in the browser version, so heroesUrl remains relative.

Universal 模板引擎link

Universal template enginelink

server.ts 文件中最重要的部分是 ngExpressEngine() 函数：

The important bit in the server.ts file is the ngExpressEngine() function.

      
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      app.engine('html', ngExpressEngine({
  bootstrap: AppServerModuleNgFactory,
  providers: [
    provideModuleMap(LAZY_MODULE_MAP)
  ]
}));
    

ngExpressEngine() 是对 Universal 的 renderModuleFactory() 函数的封装。它会把客户端请求转换成服务端渲染的 HTML 页面。 你还要在某个适用于你服务端技术栈的模板引擎中调用这个函数。

The ngExpressEngine() function is a wrapper around Universal's renderModuleFactory() function which turns a client's requests into server-rendered HTML pages. You'll call that function within a template engine that's appropriate for your server stack.

• 第一个参数是 AppServerModule。 它是 Universal 服务端渲染器和你的应用之间的桥梁。

  The first parameter is AppServerModule. It's the bridge between the Universal server-side renderer and your application.

• 第二个参数 extraProviders 是可选的。它能让你指定一些在服务端运行时特有的服务提供商。 只有当你的应用需要一些运行在服务器中才需要的信息时，才需要这么做。 这个例子中所需的信息就是正在运行的服务器的源地址，它通过 APP_BASE_HREF 令牌提供，以便应用可以 计算出 HTTP URL 的绝对地址。

  The second parameter, extraProviders, is optional. It lets you specify dependency providers that apply only when running on this server. You can do this when your app needs information that can only be determined by the currently running server instance. The required information in this case is the running server's origin, provided under the APP_BASE_HREF token, so that the app can calculate absolute HTTP URLs.

ngExpressEngine() 函数返回了一个会解析成渲染好的页面的承诺（Promise）。

The ngExpressEngine() function returns a Promise callback that resolves to the rendered page.

接下来你的引擎要决定拿这个页面做点什么。 在这个引擎的 Promise 回调函数中，把渲染好的页面返回给了 Web 服务器，然后服务器通过 HTTP 响应把它转发给了客户端。

It's up to your engine to decide what to do with that page. This engine's Promise callback returns the rendered page to the web server, which then forwards it to the client in the HTTP response.

过滤请求的 URLlink

Filtering request URLslink

Web 服务器必须把对应用页面的请求和其它类型的请求区分开。

The web server must distinguish app page requests from other kinds of requests.

这可不像拦截对根路径 / 的请求那么简单。 浏览器可以请求应用中的任何一个路由地址，比如 /dashboard、/heroes 或 /detail:12。 事实上，如果应用只会通过服务器渲染，那么应用中点击的任何一个链接都会发到服务器，就像导航时的地址会发到路由器一样。

It's not as simple as intercepting a request to the root address /. The browser could ask for one of the application routes such as /dashboard, /heroes, or /detail:12. In fact, if the app were only rendered by the server, every app link clicked would arrive at the server as a navigation URL intended for the router.

幸运的是，应用的路由具有一些共同特征：它们的 URL 一般不带文件扩展名。 （数据请求也可能缺少扩展名，但是它们很容易识别出来，因为它们总是以 /api 开头，所有的静态资源的请求都会带有一个扩展名，比如 main.js 或 /node_modules/zone.js/dist/zone.js）。

Fortunately, application routes have something in common: their URLs lack file extensions. (Data requests also lack extensions but they're easy to recognize because they always begin with /api.) All static asset requests have a file extension (such as main.js or /node_modules/zone.js/dist/zone.js).

由于使用了路由，所以我们可以轻松的识别出这三种类型的请求，并分别处理它们。

Because we use routing, we can easily recognize the three types of requests and handle them differently.

1. 数据请求 - 请求的 URL 用 /api 开头

   Data request - request URL that begins /api.

2. 应用导航 - 请求的 URL 不带扩展名

   App navigation - request URL with no file extension.

3. 静态资源 - 所有其它请求。

   Static asset - all other requests.

Node Express 服务器是一系列中间件构成的管道，它会挨个对 URL 请求进行过滤和处理。 你可以调用 app.get() 来配置 Express 服务器的管道，就像下面这个数据请求一样：

A Node Express server is a pipeline of middleware that filters and processes URL requests one after the other. You configure the Node Express server pipeline with calls to app.get() like this one for data requests.

      
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      // TODO: implement data requests securely
app.get('/api/*', (req, res) => {
  res.status(404).send('data requests are not supported');
});
    

下列代码会过滤出不带扩展名的 URL，并把它们当做导航请求进行处理。

The following code filters for request URLs with no extensions and treats them as navigation requests.

      
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      // All regular routes use the Universal engine
app.get('*', (req, res) => {
  res.render('index', { req });
});
    

安全的提供静态文件link

Serving static files safelylink

单独的 app.use() 会处理所有其它 URL，比如对 JavaScript 、图片和样式表等静态资源的请求。

A single app.use() treats all other URLs as requests for static assets such as JavaScript, image, and style files.

要保证客户端只能下载那些允许他们访问的文件，你应该把所有面向客户端的资源文件都放在 /dist 目录下，并且只允许客户端请求来自 /dist 目录下的文件。

To ensure that clients can only download the files that they are permitted to see, put all client-facing asset files in the /dist folder and only honor requests for files from the /dist folder.

下列 Express 代码会把剩下的所有请求都路由到 /dist 目录下，如果文件未找到，就会返回 404 - NOT FOUND。

The following Node Express code routes all remaining requests to /dist, and returns a 404 - NOT FOUND error if the file isn't found.

      
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      // Server static files from /browser
app.get('*.*', express.static(join(DIST_FOLDER, 'browser')));
    

Universal 实战link

Universal in actionlink

打开浏览器，访问 http://localhost:4000/。 你会看到熟悉的《英雄指南》仪表盘页。

Open a browser to http://localhost:4000/. You should see the familiar Tour of Heroes dashboard page.

通过 routerLinks 进行导航可以正常工作了。 你可以从仪表盘前往英雄列表页，也可以返回。 也可以点击仪表盘页面上的一位英雄，并显示器详情页。

Navigation via routerLinks works correctly. You can go from the Dashboard to the Heroes page and back. You can click a hero on the Dashboard page to display its Details page.

但要注意，点击、鼠标移动和键盘操作都是不行的。

Notice, however, that clicks, mouse-moves, and keyboard entries are inert.

• 点击英雄列表页中的英雄没反应。

  Clicking a hero on the Heroes page does nothing.

• 你也不能添加或删除英雄。

  You can't add or delete a hero.

• 仪表盘页面上的搜索框不理你。

  The search box on the Dashboard page is ignored.

• 详情页中的 Back 和 Save 按钮也没反应。

  The Back and Save buttons on the Details page don't work.

除了点击 RouterLink 之外的用户事件都不支持。你必须等待完整的客户端应用就绪。 直到你编译出了客户端应用，并把它们的输出移到 dist/ 目录下之后，这个客户端应用才会就绪。

User events other than routerLink clicks aren't supported. You must wait for the full client app to arrive. It won't arrive until you compile the client app and move the output into the dist/ folder.

在开发机上，从服务端渲染应用到客户端应用的转换完成的太快了。 你可以模拟一个慢速网络，来把这个转换过程看得更清楚一点，以便更好地欣赏在性能低、网络烂的设备上 Universal 应用的启动速度优势。

The transition from the server-rendered app to the client app happens quickly on a development machine. You can simulate a slower network to see the transition more clearly and better appreciate the launch-speed advantage of a Universal app running on a low-powered, poorly connected device.

打开 Chrome 开发工具，并打开 Network 页。 在菜单栏的最右侧找到 Network Throttling（网络限流） 下拉框。

Open the Chrome Dev Tools and go to the Network tab. Find the Network Throttling dropdown on the far right of the menu bar.

随便试一个 “3G” 速度。 服务端渲染的应用将会立即启动，不过加载完整的客户端应用可能要花几秒钟。

Try one of the "3G" speeds. The server-rendered app still launches quickly but the full client app may take seconds to load.