Worker threads in JavaScript

Real parallelism for CPU work, with messages between the threads.

import { Worker, isMainThread, parentPort, workerData }
  from "node:worker_threads";

const source = `
  import { parentPort, workerData } from "node:worker_threads";
  let total = 0;
  for (let i = 1; i <= workerData.limit; i += 1) total += i;
  parentPort.postMessage(total);
`;

if (isMainThread) {
  const worker = new Worker(new URL(`data:text/javascript,${source}`), {
    workerData: { limit: 1000 },
  });
  worker.on("message", (total) => console.log("worker said", total));
  worker.on("error", (error) => console.log("worker failed", error.message));
} else {
  parentPort.postMessage(workerData);
}

How it works

1. The worker runs a separate module with its own event loop.
2. workerData passes the input; postMessage returns the result.
3. Use it for CPU work, not for IO, which is already concurrent.

Keywords and builtins used here

• const
• else
• from
• if
• import

The run, in numbers

Lines

19

Characters to type

587

Tokens

110

Three-star pace

110 tpm

At the three-star pace of 110 tokens a minute, this run takes about 60 seconds.

Type this snippet

Step 3 of 3 in Crypto & processes, step 17 of 18 in Node.js.

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