Within a worker thread, worker.getEnvironmentData() returns a clone of data passed to the spawning thread's worker.setEnvironmentData(). Every new Worker receives its own copy of the environment data automatically.

import {
  Worker,
  isMainThread,
  setEnvironmentData,
  getEnvironmentData,
} from 'node:worker_threads';

if (isMainThread) {
  setEnvironmentData('Hello', 'World!');
  const worker = new Worker(__filename);
} else {
  console.log(getEnvironmentData('Hello'));  // Prints 'World!'.
}