Node.js Worker Threads: True Multi-Threading

The Single-Thread Bottleneck

Node.js handles thousands of concurrent I/O operations (like database queries or API calls) perfectly using the Event Loop. However, if you give Node.js a heavy CPU task—like processing a massive 1GB CSV file, resizing an image, or encrypting data—the single thread completely blocks. Every other user connected to your server will hang until the processing finishes.

Enter Worker Threads

Introduced natively in Node 12, the worker_threads module allows you to execute JavaScript in parallel. Unlike Python's multiprocessing which creates heavy, entirely separate OS processes, Node's Worker Threads share the same memory space (using SharedArrayBuffer), making them incredibly lightweight and fast to spin up.

When NOT to Use Them

Do not use a Worker Thread to make an HTTP request or query a database. The standard async Event Loop is infinitely better at that. Only use Worker Threads when your code involves heavy, synchronous mathematics or data parsing. Offload the math to the worker, let the main thread keep serving HTML, and have the worker send a message back when it finishes.