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Frequently Used Modules

Prerequisites

A basic understanding of Bootstrapping.

An Angular app needs at least one module that serves as the root module. As you add features to your app, you can add them in modules. The following are frequently used Angular modules with examples of some of the things they contain:

`NgModule`	`Import it from`	`Why you use it`
`<code>BrowserModule</code>`	`<code>@angular/platform-browser</code>`	`When you want to run your app in a browser`
`<code>CommonModule</code>`	`<code>@angular/common</code>`	`When you want to use <code>NgIf</code>, <code>NgFor</code>`
`<code>FormsModule</code>`	`<code>@angular/forms</code>`	`When you build template driven forms (includes <code>NgModel</code>)`
`<code>ReactiveFormsModule</code>`	`<code>@angular/forms</code>`	`When building reactive forms`
`<code>RouterModule</code> <code>RouterModule</code>（路由器模块）`	`<code>@angular/router</code>`	`For Routing and when you want to use <code>RouterLink</code>,<code>.forRoot()</code>, and <code>.forChild()</code>`
`<code>HttpClientModule</code>`	`<code>@angular/common/http</code>`	`When you to talk to a server`

Importing modules

When you use these Angular modules, import them in AppModule, or your feature module as appropriate, and list them in the @NgModule imports array. For example, in the basic app generated by the CLI, BrowserModule is the first import at the top of the AppModule, app.module.ts.


/* import modules so that AppModule can access them */
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

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

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [ /* add modules here so Angular knows to use them */
    BrowserModule,
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

The imports at the top of the array are JavaScript import statements while the imports array within @NgModule is Angular specific. For more information on the difference, see JavaScript Modules vs. NgModules.

`BrowserModule` and `CommonModule`

BrowserModule imports CommonModule, which contributes many common directives such as ngIf and ngFor. Additionally, BrowserModule re-exports CommonModule making all of its directives available to any module that imports BrowserModule.

For apps that run in the browser, import BrowserModule in the root AppModule because it provides services that are essential to launch and run a browser app. BrowserModule’s providers are for the whole app so it should only be in the root module, not in feature modules. Feature modules only need the common directives in CommonModule; they don’t need to re-install app-wide providers.

If you do import BrowserModule into a lazy loaded feature module, Angular returns an error telling you to use CommonModule instead.

More on NgModules

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