Web Workers Integration

Web Workers keep expensive computations off Aurelia’s main thread. The current Aurelia starter uses Vite, which natively supports bundling workers via the new Worker(new URL(...), { type: 'module' }) pattern. The following steps show how to add a TypeScript worker, exchange messages safely, and keep TypeScript aware of worker modules.

1. Ensure TypeScript knows about worker APIs

Update tsconfig.json (or tsconfig.app.json) so the lib array includes webworker alongside dom:

{
  "compilerOptions": {
    "lib": ["dom", "dom.iterable", "esnext", "webworker"],
    "types": []
  }
}

This gives the worker file access to self, postMessage, and related types without pulling in Node globals.

2. Create a worker entry file

// src/workers/fibonacci.worker.ts
/// <reference lib="webworker" />

function fibonacci(n: number): number {
  if (n <= 1) return n;
  return fibonacci(n - 1) + fibonacci(n - 2);
}

self.onmessage = (event: MessageEvent<number>) => {
  const input = event.data;
  const result = fibonacci(input);
  self.postMessage(result);
};

3. Wrap worker creation for DI-friendly usage

Vite exposes worker URLs via new URL('./file', import.meta.url). Export a factory that returns a strongly typed worker instance:

// src/workers/create-fibonacci-worker.ts
export function createFibonacciWorker(): Worker {
  return new Worker(new URL('./fibonacci.worker.ts', import.meta.url), {
    type: 'module',
  });
}

4. Declare a module type for worker imports (optional)

If your tooling complains when importing worker URLs, add a declaration file:

// src/types/worker.d.ts
declare module '*?worker&inline' {
  const workerConstructor: { new(): Worker };
  export default workerConstructor;
}

(With the new URL('./worker', import.meta.url) pattern this is usually unnecessary, but keep the declaration if your editor requires it.)

5. Use the worker inside an Aurelia component

// src/components/my-component.ts
import { ICustomElementViewModel } from 'aurelia';
import { createFibonacciWorker } from '../workers/create-fibonacci-worker';

export class MyComponent implements ICustomElementViewModel {
  result: number | null = null;
  private worker: Worker | null = null;

  startWorker(input: number) {
    this.disposeWorker();
    this.worker = createFibonacciWorker();
    this.worker.onmessage = (ev: MessageEvent<number>) => {
      this.result = ev.data;
      this.disposeWorker();
    };
    this.worker.onerror = (err) => {
      console.error('Worker error', err);
      this.disposeWorker();
    };
    this.worker.postMessage(input);
  }

  detaching() {
    this.disposeWorker();
  }

  private disposeWorker() {
    this.worker?.terminate();
    this.worker = null;
  }
}

<!-- src/components/my-component.html -->
<template>
  <input type="number" value.bind="userInput" debounce="200">
  <button click.trigger="startWorker(+userInput || 0)">Calculate Fibonacci</button>
  <p if.bind="result !== null">Worker result: ${result}</p>
</template>

6. Sharing types between main thread and worker

Create a shared interface so both sides agree on message shapes:

// src/workers/messages.ts
export type WorkerRequest = { kind: 'fibonacci'; value: number };
export type WorkerResponse = { kind: 'fibonacci'; result: number };

Use those types inside the worker and component for additional safety.

7. Debugging tips

• Use worker.postMessage({}) only with structured-cloneable data (objects, ArrayBuffers, typed arrays). Avoid functions or DOM nodes.

• Workers live in their own file scope—import only what you need. Vite will tree-shake unused code.

• If you need multiple workers, create helper factories (createImageWorker, createSearchWorker, etc.) so components can spin them up lazily.

With this Vite-native worker setup, you avoid legacy webpack worker-loader plugins and keep Aurelia’s main thread responsive during heavy computations.