Threads can certainly run in parallel with one another if the OS schedules them on different cores. I did a quick experiment and the main thread and worker thre

Threads can certainly run in parallel with one another if the OS schedules them on different cores. I did a quick experiment and the main thread and worker threads run in parallel. https://github.com/jschaf/web-worker-experiment/ https://github.com/jschaf/web-worker-experiment/ > You don't get extra calculation performance with web workers The primary purpose of web workers is extra calculation performance. From MDN: > Workers are mainly useful for allowing your code to perform processor-intensive calculations without blocking the user interface thread