Running code using threads.js in node works out of the box.

Note that we wrap the native Worker, so new Worker("./foo/bar") will resolve the path relative to the module that calls it, not relative to the current working directory.

That aligns it with the behavior when bundling the code with webpack or parcel.

Webpack config

Use with the threads-plugin. It will transparently detect all new Worker("./unbundled-path") expressions, bundles the worker code and replaces the new Worker(...) path with the worker bundle path, so you don't need to explicitly use the worker-loader or define extra entry points.

  npm install -D threads-plugin

Then add it to your webpack.config.js:

+ const ThreadsPlugin = require('threads-plugin');

  module.exports = {
    // ...
    plugins: [
+     new ThreadsPlugin()
    ]
    // ...
  }

Node.js bundles

If you are using webpack to create a bundle that will be run in node (webpack config target: "node"), you also need to specify that the tiny-worker package used for node < 12 should not be bundled:

  module.exports = {
    // ...
+   externals: {
+     "tiny-worker": "tiny-worker"
+   }
    // ...
}

Make sure that tiny-worker is listed in your package.json dependencies in that case.

When using TypeScript

Note: You'll need to be using Typescript version 4+, as the types generated by threads.js are not supported in Typescript 3.

Make sure the TypeScript compiler keeps the import / export statements intact, so webpack resolves them. Otherwise the threads-plugin won't be able to do its job.

  module.exports = {
    // ...
    module: {
      rules: [
        {
          test: /\.ts$/,
          loader: "ts-loader",
+         options: {
+           compilerOptions: {
+             module: "esnext"
+           }
+         }
        }
      ]
    },
    // ...
  }

You need to import threads/register once at the beginning of your application code (in the master code, not in the workers):

  import { spawn } from "threads"
+ import "threads/register"

  // ...

  const work = await spawn(new Worker("./worker"))

This registers the library's Worker implementation for your platform as the global Worker. This is necessary, since you cannot import { Worker } from "threads" or Parcel won't recognize new Worker() as a web worker anymore.

Be aware that this might affect any code that tries to instantiate a normal web worker Worker and now instead instantiates a threads.js Worker. The threads.js Worker is just a web worker with some sugar on top, but that sugar might have unexpected side effects on third-party libraries.

Everything else should work out of the box.