AppModule: 根模块

Angular 模块类描述应用的部件是如何组合在一起的。 每个应用都至少有一个 Angular 模块，也就是根模块，用来引导并运行应用。 你可以为它取任何名字。常规名字是AppModule。

An Angular module class describes how the application parts fit together. Every application has at least one Angular module, the root module that you bootstrap to launch the application. You can call it anything you want. The conventional name is AppModule.

开发环境讲解了如何使用下面这个最小的AppModule来创建一个新项目。 这个模块随着应用的成长而演变。

The setup instructions produce a new project with the following minimal AppModule. You'll evolve this module as your application grows.

import { NgModule }      from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent }  from './app.component';

@NgModule({
  imports:      [ BrowserModule ],
  declarations: [ AppComponent ],
  bootstrap:    [ AppComponent ]
})
export class AppModule { }

import语句之后，可以看到一个@NgModule装饰器修饰的类。

After the import statements, you come to a class adorned with the @NgModule decorator.

@NgModule装饰器将AppModule标记为 Angular 模块类（也叫NgModule类）。 @NgModule接受一个元数据对象，告诉 Angular 如何编译和启动应用。

The @NgModule decorator identifies AppModule as an Angular module class (also called an NgModule class). @NgModule takes a metadata object that tells Angular how to compile and launch the application.

• imports — BrowserModule，这个和每个在浏览器中运行应用都需要它。

  imports — the BrowserModule that this and every application needs to run in a browser.

• declarations — 应用的唯一组件，它同时也是...

  declarations — the application's lone component, which is also ...

• bootstrap — 根组件，Angular 创建它并插入index.html宿主页面。

  bootstrap — the root component that Angular creates and inserts into the index.html host web page.

Angular 模块 (NgModules) 指南深入讲解了 Angular 模块。 现在先初步了解这三个属性。

The Angular Modules (NgModule) guide dives deeply into the details of Angular modules. All you need to know at the moment is a few basics about these three properties.

imports 数组

The imports array

Angular 模块把特性合并成离散单元的一种方式。 Angular 自身的许多特性也是通过 Angular 模块组织的。 HTTP 服务在HttpModule里。路由器在RouterModule中。 最终，你可能也会创建特性模块。

Angular modules are a way to consolidate features that belong together into discrete units. Many features of Angular itself are organized as Angular modules. HTTP services are in the HttpModule. The router is in the RouterModule. Eventually you may create a feature module.

当应用需要模块的特性时，将其添加到imports数组中。

Add a module to the imports array when the application requires its features.

这个应用和大多数其他应用一样，在浏览器中运行。 每个浏览器中运行的应用都需要@angular/platform-browser里的BrowserModule。 所以每个这样的应用都在其根AppModule的imports数组中包含BrowserModule。 在需要添加额外模块到此数组时，其他指南和烹饪宝典页面会告诉你。

This application, like most applications, executes in a browser. Every application that executes in a browser needs the BrowserModule from @angular/platform-browser. So every such application includes the BrowserModule in its root AppModule's imports array. Other guide and cookbook pages will tell you when you need to add additional modules to this array.

declarations 数组

The declarations array

通过将其列到AppModule模块的declarations数组中，可以告诉 Angular 哪个组件属于AppModule。 在创建更多组件的过程中，逐步将它们添加到declarations中。

You tell Angular which components belong to the AppModule by listing it in the module's declarations array. As you create more components, you'll add them to declarations.

你必须在一个NgModule类声明每一个组件。 否则当你使用这些组件时就会在浏览器的控制台中看到一个明显的错误信息。

You must declare every component in an NgModule class. If you use a component without declaring it, you'll see a clear error message in the browser console.

你将会学习如何创建其他两种类 — 指令和管道 — 它们也必须被添加到declarations数组。

You'll learn to create two other kinds of classes — directives and pipes — that you must also add to the declarations array.

bootstrap 数组

The bootstrap array

通过引导根AppModule来启动应用。 在启动过程中，其中一步是创建列在bootstrap数组的组件， 并将它们每一个都插入到浏览器的DOM中。

You launch the application by bootstrapping the root AppModule. Among other things, the bootstrapping process creates the component(s) listed in the bootstrap array and inserts each one into the browser DOM.

每个被引导的组件都是它自己的组件树的根。 插入一个被引导的组件通常触发一系列组件的创建并形成组件树。

Each bootstrapped component is the base of its own tree of components. Inserting a bootstrapped component usually triggers a cascade of component creations that fill out that tree.

虽然你可以将多个组件树插入到宿主页面，但并不普遍。 大多数应用只有一个组件树，它们引导单一根组件。

While you can put more than one component tree on a host web page, that's not typical. Most applications have only one component tree and they bootstrap a single root component.

你可以为这个根组件取任何名字，但是大多数程序员将其取名为AppComponent。

You can call the one root component anything you want but most developers call it AppComponent.

下面让我们来看看引导过程本身。

Which brings us to the bootstrapping process itself.

在main.ts中引导

Bootstrap in main.ts

引导应用的方法很多。 它们取决于你想如何编译应用以及应用将在哪儿运行。

There are many ways to bootstrap an application. The variations depend upon how you want to compile the application and where you want to run it.

开始时，你将使用即时 (JiT) 编译器动态编译应用。然后在浏览器中运行它。 稍后，你可以了解其他选项。

In the beginning, you will compile the application dynamically with the Just-in-Time (JIT) compiler and you'll run it in a browser. You can learn about other options later.

引导即时编译的浏览器应用的推荐地点是在src目录中一个名为src/main.ts的单独文件中。

The recommended place to bootstrap a JIT-compiled browser application is in a separate file in the src folder named src/main.ts

import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { AppModule }              from './app/app.module';

platformBrowserDynamic().bootstrapModule(AppModule);

上面的代码为动态 (JiT) 编译创建浏览器平台，并引导上面提到的AppModule。

This code creates a browser platform for dynamic (JIT) compilation and bootstraps the AppModule described above.

引导过程搭建运行环境，从模块的bootstrap数组中提出根AppComponent， 创建该组件的实例，并将其插入到组件selector标识的元素标签中。

The bootstrapping process sets up the execution environment, digs the root AppComponent out of the module's bootstrap array, creates an instance of the component and inserts it within the element tag identified by the component's selector.

AppComponent选择器 — 在这里以及文档大部分例子中 — 是my-app， 所以 Angular 在index.html中查找像这样的<my-app>标签...

The AppComponent selector — here and in most documentation samples — is my-app so Angular looks for a <my-app> tag in the index.html like this one ...

<my-app><!-- content managed by Angular --></my-app>

...然后在那儿显示AppComponent。

... and displays the AppComponent there.

该文件非常稳定。一旦配置好，你可能永远不会再修改它。

This file is very stable. Once you've set it up, you may never change it again.

关于Angular模块的更多知识

More about Angular Modules

你最初的应用只有一个单一的模块 —— 根模块。 当这个应用不断成长时，你就要考虑把它们拆分到多个 "特性" 模块中了。 这些特性模块中的一部分可以稍后加载（即惰性加载），它们只会在用户访问到这些特性时才会加载。

Your initial app has only a single module, the root module. As your app grows, you'll consider subdividing it into multiple "feature" modules, some of which can be loaded later ("lazy loaded") if and when the user chooses to visit those features.

如果你要了解这些知识，请访问Angular 模块 (NgModule)页

When you're ready to explore these possibilities, visit the Angular Modules (NgModule) guide.