How to Manage CPU-Intensive Tasks in JavaScript

JavaScript is single-threaded, meaning it can execute only one task at a time.

Promises and async/await do enable JavaScript to execute asynchronous tasks, but they don’t make JavaScript multi-threaded. Instead, they allow JavaScript to handle non-blocking operations without pausing the main thread.

It's like a restaurant with a single cook—the chef can manage multiple dishes on the stove, in the oven, and in the microwave simultaneously, but when it comes to actively preparing ingredients or plating food, they can handle only one dish at a time.

This approach works particularly well for I/O or networking tasks, like fetching data from an API or reading files, where most of the waiting happens in external systems outside JavaScript itself.

But what happens when you have computation-heavy tasks—like processing a massive array or performing complex mathematical operations—that hog the CPU for a significant amount of time (1–2 minutes, for instance)?

For such CPU-intensive tasks, a single-threaded approach can become a bottleneck because the JavaScript engine is confined to executing one task at a time.

To handle such workloads efficiently, we need a way to offload tasks to multiple threads or CPU cores, allowing the load to be divided and processed concurrently.

Can JavaScript handle this kind of parallelism?

This challenge can be addressed by using Web Workers (in browsers) or Worker Threads (in Node.js). These workers operate as separate threads that execute your CPU-intensive tasks in parallel, independent of the main thread.

This approach prevents your application from freezing or becoming unresponsive, as the main thread remains free to handle user interactions, rendering, or other tasks while the workers perform their computations.

By identifying tasks that are heavy on the CPU and offloading them to Workers, you can make your application faster and more responsive.