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Node.js › Clustering & Worker Threads

What is the WorkerData option when creating a Worker, and how does it differ from communicating via postMessage() after creation?

Advanced

Answer

workerData is a value passed once, synchronously, at Worker construction time, immediately available inside the worker without waiting for an initial message -- useful for initial configuration, whereas postMessage() is used for ongoing communication after the worker is already running.
if (isMainThread) {
  const worker = new Worker(__filename, { workerData: { inputFile: 'data.csv' } });
} else {
  console.log('Processing:', workerData.inputFile);
}
Real-world example A batch-processing worker receives its input file path via workerData at creation, needing no initial handshake before beginning work, while using postMessage() afterward for progress updates.

Common follow-ups: Why can't workerData be used for ongoing communication after the worker has started?;What happens if workerData contains a value that can't be structured-cloned, like a function?

Advanced Node.js;Background Jobs & Queues
All 15 Clustering & Worker Threads questions