63 lines
2.4 KiB
Markdown
63 lines
2.4 KiB
Markdown
# 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,
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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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<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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To add a web worker to an existing project, use the Angular CLI `ng generate` command.
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```bash
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ng generate web-worker <location>
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```
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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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```bash
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ng generate web-worker app
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```
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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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const response = `worker response to ${data}`;
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postMessage(response);
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});
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</code-example>
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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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// Create a new
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const worker = new Worker('./app.worker', { type: 'module' });
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worker.onmessage = ({ data }) => {
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console.log(`page got message: ${data}`);
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};
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worker.postMessage('hello');
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} else {
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// Web workers are not supported in this environment.
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// You should add a fallback so that your program still executes correctly.
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}
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</code-example>
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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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<div class="alert is-important">
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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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</div>
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