118 lines
6.0 KiB
Markdown
118 lines
6.0 KiB
Markdown
# Feature Modules
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Feature modules are NgModules for the purpose of organizing code.
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For the final sample app with a feature module that this page describes,
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see the <live-example></live-example>.
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<hr>
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As your app grows, you can organize code relevant for a specific feature.
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This helps apply clear boundaries for features. With feature modules,
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you can keep code related to a specific functionality or feature
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separate from other code. Delineating areas of your
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app helps with collaboration between developers and teams, separating
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directives, and managing the size of the root module.
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## Feature modules vs. root modules
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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
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specific application need such as a user workflow, routing, or forms.
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While you can do everything within the root module, feature modules
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help you partition the app into focused areas. A feature module
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collaborates with the root module and with other modules through
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the services it provides and the components, directives, and
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pipes that it shares.
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## How to make a feature module
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Assuming you already have an app that you created with the [Angular CLI](cli), create a feature
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module using the CLI by entering the following command in the
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root project directory. Replace `CustomerDashboard` with the
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name of your module. You can omit the "Module" suffix from the name because the CLI appends it:
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```sh
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ng generate module CustomerDashboard
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```
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This causes the CLI to create a folder called `customer-dashboard` with a file inside called `customer-dashboard.module.ts` with the following contents:
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```typescript
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import { NgModule } from '@angular/core';
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import { CommonModule } from '@angular/common';
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@NgModule({
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imports: [
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CommonModule
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],
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declarations: []
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})
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export class CustomerDashboardModule { }
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```
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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.
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The `declarations` array is available for you to add declarables, which
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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:
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```sh
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ng generate component customer-dashboard/CustomerDashboard
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```
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This generates a folder for the new component within the customer-dashboard folder and updates the feature module with the `CustomerDashboardComponent` info:
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<code-example path="feature-modules/src/app/customer-dashboard/customer-dashboard.module.ts" region="customer-dashboard-component" header="src/app/customer-dashboard/customer-dashboard.module.ts"></code-example>
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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.
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## Importing a feature module
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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:
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<code-example path="feature-modules/src/app/app.module.ts" region="app-module" header="src/app/app.module.ts"></code-example>
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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.
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## Rendering a feature module’s component template
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When the CLI generated the `CustomerDashboardComponent` for the feature module, it included a template, `customer-dashboard.component.html`, with the following markup:
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<code-example path="feature-modules/src/app/customer-dashboard/customer-dashboard/customer-dashboard.component.html" region="feature-template" header="src/app/customer-dashboard/customer-dashboard/customer-dashboard.component.html"></code-example>
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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 `CustomerDashboardComponent`:
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<code-example path="feature-modules/src/app/customer-dashboard/customer-dashboard.module.ts" region="component-exports" header="src/app/customer-dashboard/customer-dashboard.module.ts"></code-example>
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Next, in the `AppComponent`, `app.component.html`, add the tag `<app-customer-dashboard>`:
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<code-example path="feature-modules/src/app/app.component.html" region="app-component-template" header="src/app/app.component.html"></code-example>
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Now, in addition to the title that renders by default, the `CustomerDashboardComponent` template renders too:
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<figure>
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<img src="generated/images/guide/feature-modules/feature-module.png" alt="feature module component">
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</figure>
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<hr />
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## More on NgModules
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You may also be interested in the following:
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* [Lazy Loading Modules with the Angular Router](guide/lazy-loading-ngmodules).
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* [Providers](guide/providers).
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* [Types of Feature Modules](guide/module-types).
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