The App shell pattern 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.
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  Prepare the applicationDo this with the following Angular CLI command: ng new my-appFor an existing application, you have to manually add the Routerand defining a<router-outlet>within your application.
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  Create the application shellUse the Angular CLI to automatically create the application shell. ng generate app-shellFor more information about this command, see App shell command. The command updates the application code and adds extra files to the project structure. srcâââ appâ âââ app.config.server.ts # server application configurationâ âââ app-shell # app-shell componentâ âââ app-shell.component.htmlâ âââ app-shell.component.scssâ âââ app-shell.component.spec.tsâ âââ app-shell.component.tsâââ main.server.ts # main server application bootstrappingng build --configuration=developmentOr to use the production configuration. ng buildTo verify the build output, open dist/my-app/browser/index.html. Look for default textapp-shell works!to show that the application shell route was rendered as part of the output.