Worker threads — what do you do with an expensive computation?

Worker threads run JavaScript on extra threads and are useful for expensive CPU work. The main event loop can then keep handling I/O.

Example: I move a large report calculation to a pool of workers and pass the job through messages. I don't create a new worker for every small operation.

To be precise: a child process has its own process and memory. Workers can share memory through SharedArrayBuffer, but the simplest model is messages with copied or transferred data.

Pitfall: plain async doesn't move CPU work to a worker. For typical I/O an extra worker often doesn't help, because Node already has asynchronous mechanisms.