vitest fails to load typescript worker code in node (but does so correctly in browser mode) about vitest HOT 6 CLOSED

Oh right, tsx probably spawns extra process in between, so Node's out-of-the-box worker communication doesn't work.

Just reading back the original Node issue nodejs/node#47747 (comment), it might be that the fix is near in Node 22, but I just double checked it still doesn't work (and it actually breaks more for some use cases).

For the workaround on Node 20, I think you can use tsx/esm/api like this to wrap your worker. I just tested this approach here https://github.com/hi-ogawa/reproductions/blob/main/vitest-5757-ts-worker/src/ts-worker/index.mjs

import { Worker } from "node:worker_threads";

class TsWorker extends Worker {
  constructor(filename, options = {}) {
    options.workerData ??= {};
    options.workerData.__ts_worker_filename = filename.toString();
    super(new URL("./worker.mjs", import.meta.url), options);
  }
}

const worker = new TsWorker(new URL("./your-actual-worker.ts", import.meta.url));

// worker.mjs
import { tsImport } from "tsx/esm/api";
import { workerData } from "node:worker_threads";

tsImport(workerData.__ts_worker_filename, import.meta.url);

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Browser mode is quite different and it just happens that Vite's web worker support makes it work, but I don't think the same technique naturally transfers to node worker threads. It's unlikely to have some magical feature on Vitest out-of-the-box as noted in #3234 (comment)

Regarding tsx loader failing on Worker constructor, this seems like a well known issue/limitation of current Node loader:

• privatenumber/tsx#354
• nodejs/node#47747

The tsx issue suggests one workaround privatenumber/tsx#354 (comment) and that would probably work.

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The equivalent cannot work just fine in the browser mode because the browser mode doesn't support node:worker_threads module.

If you are testing web worker, the recommendation is to use @vitest/web-worker package.

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The equivalent cannot work just fine in the browser mode because the browser mode doesn't support node:worker_threads module.

With equivalent code I meant code implemented in terms of web worker, see test-browser script.

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For anyone landing here looking for a solution: I didn't get it to work. I tried with the following lines

        const tsx = new URL("../node_modules/tsx/dist/cli.mjs", import.meta.url);
        const worker = new Worker(tsx, { env: SHARE_ENV, argv: ["./src/nodeWorker.ts"] });

Both cli.mjs and nodeWorker.ts are found, but apparently the message posted on the main thread never makes it to the worker.

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For the workaround on Node 20, I think you can use tsx/esm/api like this to wrap your worker.

Indeed, that works. I've modified vitest-repro accordingly and adapted the instructions for the reproduction to check out the original code.

Thank you very much!

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