angular-cn/aio/content/guide/feature-modules.md

# Feature Modules

Feature modules are NgModules for the purpose of  organizing code.

#### Prerequisites
A basic understanding of the following:
* [Bootstrapping](guide/bootstrapping).
* [JavaScript Modules vs. NgModules](guide/ngmodule-vs-jsmodule).
* [Frequently Used Modules](guide/frequent-ngmodules).

For the final sample app with a feature module that this page describes,
see the <live-example></live-example>.

<hr>

As your app grows, you can organize code relevant for a specific feature.
This helps apply clear boundaries for features. With feature modules,
you can keep code related to a specific functionality or feature
separate from other code. Delineating areas of your
app helps with collaboration between developers and teams, separating
directives, and managing the size of the root module.


## Feature modules vs. root modules

A feature module is an organizational best practice, as opposed to a concept of the core Angular API. A feature module delivers a cohesive set of functionality focused on a
specific application need such as a user workflow, routing, or forms.
While you can do everything within the root module, feature modules
help you partition the app into focused areas. A feature module
collaborates with the root module and with other modules through
the services it provides and the components, directives, and
pipes that it shares.

## How to make a feature module

Assuming you already have a CLI generated app, create a feature
module using the CLI by entering the following command in the
root project directory. Replace `CustomerDashboard` with the
name of your module. You can omit the word module because the CLI appends it:

```sh
ng generate module CustomerDashboard

```


This causes the CLI to create a folder called `customer-dashboard` with a file inside called `customer-dashboard.module.ts` with the following contents:

```ts

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';

@NgModule({
 imports: [
   CommonModule
 ],
 declarations: []
})

export class CustomerDashboardModule { }


```

The structure of an NgModule is the same whether it is a root module or a feature module. In the CLI generated feature module, there are two JavaScript import statements at the top of the file: the first imports `NgModule`, which, like the root module, lets you use the `@NgModule` decorator; the second imports `CommonModule`, which contributes many common directives such as `ngIf` and `ngFor`. Feature modules import `CommonModule` instead of `BrowserModule`, which is only imported once in the root module. `CommonModule` only contains information for common directives such as `ngIf` and `ngFor` which are needed in most templates, whereas `BrowserModule` configures the Angular app for the browser which needs to be done only once.

The `declarations` array is available for you to add declarables, which
are components, directives, and pipes that belong exclusively to this particular module. To add a component, enter the following command at the command line where `customer-dashboard` is the directory where the CLI generated the feature module and `CustomerDashboard` is the name of the component:

```sh
ng generate component customer-dashboard/CustomerDashboard

```

This generates a folder for the new component within the customer-dashboard folder and updates the feature module with the `CustomerDashboardComponent` info:


<code-example path="feature-modules/src/app/customer-dashboard/customer-dashboard.module.ts" region="customer-dashboard-component" title="src/app/customer-dashboard.module.ts" linenums="false">
</code-example>



The `CustomerDashboardComponent` is now in the JavaScript import list at the top and added to the `declarations` array, which lets Angular know to associate this new component with this feature module.

## Importing a feature module

To incorporate the feature module into your app, you have to let the root module, `app.module.ts`, know about it. Notice the `CustomerDashboardModule` export at the bottom of `customer-dashboard.module.ts`. This exposes it so that other modules can get to it. To import it into the AppModule, add it to the imports in `app.module.ts` and to the imports array:

<code-example path="feature-modules/src/app/app.module.ts" region="app-module" title="src/app/app.module.ts" linenums="false">
</code-example>


Now the `AppModule` knows about the feature module. If you were to add any service providers to the feature module, `AppModule` would know about those too, as would any other feature modules. However, NgModules don’t expose their components.


## Rendering a feature module’s component template

When the CLI generated the `CustomerDashboardComponent` for the feature module, it included a template, `customer-dashboard.component.html`, with the following markup:

<code-example path="feature-modules/src/app/customer-dashboard/customer-dashboard/customer-dashboard.component.html" region="feature-template" title="src/app/customer-dashboard/customer-dashboard/customer-dashboard.component.html" linenums="false">
</code-example>


To see this HTML in the `AppComponent`, you first have to export the `CustomerDashboardComponent` in the `CustomerDashboardModule`. In `customer-dashboard.module.ts`, just beneath the declarations array, add an exports array containing `CustomerDashboardModule`:

<code-example path="feature-modules/src/app/customer-dashboard/customer-dashboard.module.ts" region="customer-dashboard-component" title="src/app/customer-dashboard.module.ts" linenums="false">
</code-example>



Next, in the `AppComponent`, `app.component.html`, add the tag `<app-customer-dashboard>`:

<code-example path="feature-modules/src/app/app.component.html" region="app-component-template" title="src/app/app.component.html" linenums="false">
</code-example>


Now, in addition to the title that renders by default, the `CustomerDashboardComponent` template renders too:


<figure>
 <img src="generated/images/guide/feature-modules/feature-module.png" alt="feature module component">
</figure>

<hr />

## More on NgModules

You may also be interested in the following:
* [Lazy Loading Modules with the Angular Router](guide/lazy-loading-ngmodules).
* [Providers](guide/providers).
* [Types of NgModules](guide/module-types).