web-workers.md

Background processing using web workers

Web workers let you run CPU-intensive computations in a background thread, freeing the main thread to update the user interface. Application's performing a lot of computations, like generating Computer-Aided Design (CAD) drawings or doing heavy geometric calculations, can use web workers to increase performance.

HELPFUL: The Angular CLI does not support running itself in a web worker.

Adding a web worker

To add a web worker to an existing project, use the Angular CLI ng generate command.

ng generate web-worker

You can add a web worker anywhere in your application. For example, to add a web worker to the root component, src/app/app.component.ts, run the following command.

ng generate web-worker app

The command performs the following actions.

1. Configures your project to use web workers, if it isn't already.

2. Adds the following scaffold code to src/app/app.worker.ts to receive messages.

   addEventListener('message', ({ data }) => { const response = worker response to ${data}; postMessage(response); });

3. Adds the following scaffold code to src/app/app.component.ts to use the worker.

   if (typeof Worker !== 'undefined') { // Create a new const worker = new Worker(new URL('./app.worker', import.meta.url)); worker.onmessage = ({ data }) => { console.log(page got message: ${data}); }; worker.postMessage('hello'); } else { // Web workers are not supported in this environment. // You should add a fallback so that your program still executes correctly. }

After you create this initial scaffold, you must refactor your code to use the web worker by sending messages to and from the worker.

IMPORTANT: Some environments or platforms, such as @angular/platform-server used in Server-side Rendering, don't support web workers.

To ensure that your application works in these environments, you must provide a fallback mechanism to perform the computations that the worker would otherwise perform.