95Implement a Web Worker for CPU-intensive computation

Heavy computation on the main thread freezes scrolling, typing and animations. Implement createWorkerTask(fn), which runs a self-contained function in a Web Worker and returns:

• run(...args): a promise for fn(...args) computed in the worker. Several calls may be in flight at once; each gets its own result.
• terminate(): stop the worker and reject every pending call with an error named "AbortError".

Errors thrown inside fn must reject the matching run call with an Error that has the same message. fn may be async.

Create the worker from a Blob URL, so no separate file is needed:

const primes = createWorkerTask((limit) => {
  const sieve = new Uint8Array(limit + 1);
  let count = 0;
  for (let i = 2; i <= limit; i++) {
    if (sieve[i]) continue;
    count++;
    for (let j = i * i; j <= limit; j += i) sieve[j] = 1;
  }
  return count;
});
const count = await primes.run(10_000_000); // the page stays responsive