angular-cn/aio/content/guide/app-shell.md

# App shell

App shell is a way to render a portion of your application via a route at build time.
It can improve the user experience by quickly launching a static rendered page (a skeleton common to all pages) while the browser downloads the full client version and switches to it automatically after the code loads.

This gives users a meaningful first paint of your application that appears quickly because the browser can simply render the HTML and CSS without the need to initialize any JavaScript.

Learn more in [The App Shell Model](https://developers.google.com/web/fundamentals/architecture/app-shell).

## Step 1: Prepare the application

You can do this with the following CLI command:
<code-example format="." language="bash">
ng new my-app --routing
</code-example>

For an existing application, you have to manually add the `RouterModule` and defining a `<router-outlet>` within your application.

## Step 2: Create the app shell

Use the CLI to automatically create the app shell.

<code-example format="." language="bash">
ng generate app-shell --client-project my-app --universal-project server-app
</code-example>

* `my-app` takes the name of your client application.
* `server-app` takes the name of the Universal (or server) application.

After running this command you will notice that the `angular.json` configuration file has been updated to add two new targets, with a few other changes.

<code-example format="." language="json">
"server": {
  "builder": "@angular-devkit/build-angular:server",
  "options": {
    "outputPath": "dist/my-app-server",
    "main": "src/main.server.ts",
    "tsConfig": "tsconfig.server.json"
  }
},
"app-shell": {
  "builder": "@angular-devkit/build-angular:app-shell",
  "options": {
    "browserTarget": "my-app:build",
    "serverTarget": "my-app:server",
    "route": "shell"
  }
}
</code-example>

## Step 3: Verify the app is built with the shell content

Use the CLI to build the `app-shell` target.

<code-example format="." language="bash">
ng run my-app:app-shell
</code-example>

To verify the build output, open `dist/my-app/index.html`. Look for default text `app-shell works!` to show that the app shell route was rendered as part of the output.