passing_worker_data.js

const kPublicPort = Symbol('kPublicPort');
// ...redacted...

const { port1, port2 } = new MessageChannel();
this[kPublicPort] = port1;
this[kPublicPort].on('message', (message) => this.emit('message', message));
// ...redacted...

this[kPort].postMessage({
  type: 'loadScript',
  filename,
  doEval: !!options.eval,
  cwdCounter: cwdCounter || workerIo.sharedCwdCounter,
  workerData: options.workerData,
  publicPort: port2,
  // ...redacted...
  hasStdin: !!options.stdin
}, [port2]);