method Worker.postMessage

// Create a buffer to transfer (not copy) to the worker
const buffer = new ArrayBuffer(1024);
worker.postMessage({ data: buffer }, [buffer]);
// After transfer, buffer is no longer usable in the main thread

// Send a simple message with data
worker.postMessage({
  command: "process",
  data: [1, 2, 3, 4],
  settings: { optimize: true }
});