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

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# App shell
Application shell is a way to render a portion of your application using 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 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 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 application shell.
<code-example language="bash">
ng generate app-shell
</code-example>
For more information about this command see [App shell command](cli/generate#app-shell-command).
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 language="json">
"server": {
"builder": "@angular-devkit/build-angular:server",
"defaultConfiguration": "production",
"options": {
"outputPath": "dist/my-app/server",
"main": "src/main.server.ts",
"tsConfig": "tsconfig.server.json"
},
"configurations": {
"development": {
"outputHashing": "none",
},
"production": {
"outputHashing": "media",
"fileReplacements": [
{
"replace": "src/environments/environment.ts",
"with": "src/environments/environment.prod.ts"
}
],
"sourceMap": false,
"optimization": true
}
}
},
"app-shell": {
"builder": "@angular-devkit/build-angular:app-shell",
"defaultConfiguration": "production",
"options": {
"route": "shell"
},
"configurations": {
"development": {
"browserTarget": "my-app:build:development",
"serverTarget": "my-app:server:development",
},
"production": {
"browserTarget": "my-app:build:production",
"serverTarget": "my-app:server:production"
}
}
}
</code-example>
## Step 3: Verify the app is built with the shell content
Use the CLI to build the `app-shell` target.
<code-example language="bash">
ng run my-app:app-shell:development
</code-example>
Or to use the production configuration.
<code-example language="bash">
ng run my-app:app-shell:production
</code-example>
To verify the build output, open `dist/my-app/browser/index.html`. Look for default text `app-shell works!` to show that the application shell route was rendered as part of the output.