parentPort

In Node.js, parentPort is a global available to worker threads that represents the communication channel back to the spawning thread. It is a MessagePort object that enables two-way messaging between a worker and its parent.

The property exists only inside worker threads. In the main thread, there is no parentPort. To use it safely, require the worker_threads module and destructure parentPort from it, e.g., const { parentPort } = require('worker_threads'); and check if (parentPort) before using.

From the worker, messages can be sent to the parent with parentPort.postMessage(value). The worker can also receive messages by listening to the 'message' event on the port, e.g., parentPort.on('message', (msg) => { ... }). In the parent thread, a Worker instance exposes its own 'message' event for incoming data, and messages can be sent to the worker with worker.postMessage(value).

The parentPort object conforms to the MessagePort interface and can be closed with close() when communication is finished. If the worker terminates, the port becomes unusable and will no longer receive messages. This mechanism is central to coordinating work and data exchange between a Node.js parent thread and its workers.