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# Using web workers with Angular CLI
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# Background processing using web workers
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[Web workers](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API) allow you to run CPU intensive computations in a background thread, freeing the main thread to update the user interface.
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[Web workers](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API) allow you to run CPU-intensive computations in a background thread,
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freeing the main thread to update the user interface.
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If you find your application performs a lot of computations, such as generating CAD drawings or doing heavy geometrical calculations, using web workers can help increase your application's performance.
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If you find your application becomes unresponsive while processing data, using web workers can help.
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<div class="alert is-helpful>
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The CLI does not support running Angular itself in a web worker.
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</div>
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## Adding a web worker
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You can add a web worker anywhere in your application. If the file that contains your expensive computation is `src/app/app.component.ts`, you can add a web worker using `ng generate web-worker app`.
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To add a web worker to an existing project, use the Angular CLI `ng generate` command.
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Running this command will:
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`ng generate web-worker` *location*
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- configure your project to use web workers, if it isn't already.
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- add `src/app/app.worker.ts` with scaffolded code to receive messages:
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You can add a web worker anywhere in your application.
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For example, to add a web worker to the root component, `src/app/app.component.ts`, run the following command.
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`ng generate web-worker app`.
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The command performs the following actions.
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- Configures your project to use web workers, if it isn't already.
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- Adds the following scaffold code to `src/app/app.worker.ts` to receive messages.
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<code-example language="typescript" header="src/app/app.worker.ts">
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addEventListener('message', ({ data }) => {
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});
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</code-example>
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- add scaffolded code to `src/app/app.component.ts` to use the worker:
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- Adds the following scaffold code to `src/app/app.component.ts` to use the worker.
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<code-example language="typescript" header="src/app/app.component.ts">
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if (typeof Worker !== 'undefined') {
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}
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</code-example>
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After the initial scaffolding, you will need to refactor your code to use the web worker by sending messages to and from.
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After you generate this initial scaffold, you must refactor your code to use the web worker by sending messages to and from the worker.
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## Caveats
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<div class="alert is-important>
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There are two important things to keep in mind when using web workers in Angular projects:
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Some environments or platforms, such as `@angular/platform-server` used in [Server-side Rendering](guide/universal), don't support web workers. To ensure that your application will work in these environments, you must provide a fallback mechanism to perform the computations that the worker would otherwise perform.
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- Some environments or platforms, like `@angular/platform-server` used in [Server-side Rendering](guide/universal), don't support web workers. You have to provide a fallback mechanism to perform the computations that the worker would perform to ensure your application will work in these environments.
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- Running Angular itself in a web worker via [**@angular/platform-webworker**](api/platform-webworker) is not yet supported in Angular CLI.
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</div>
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@ -583,8 +583,8 @@
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},
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{
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"url": "guide/web-worker",
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"title": "Web Workers",
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"tooltip": "Using Web Workers with Angular CLI."
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"title": "Web Workers in Angular",
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"tooltip": "Implement background processing with web workers."
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}
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]
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},
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