What are Web Workers and when should you use them?

Question

What are Web Workers and when should you use them?

Answer

Web Workers allow JavaScript to run background tasks on separate threads — preventing UI blocking.

// main.js
const worker = new Worker('worker.js');
worker.postMessage(100000);

worker.onmessage = (e) => console.log('Result:', e.data);

// worker.js
onmessage = function (e) {
  let sum = 0;
  for (let i = 0; i < e.data; i++) sum += i;
  postMessage(sum);
};

Use them for:

• Heavy computations
• Image/video processing
• Data parsing or compression

Real-World Example

Used in data visualizations, ML in JS, and complex WebAssembly integrations.

Quick Practice

Create a simple Web Worker that counts to a million and sends the result back to the main thread.

Summary

Web Workers = background multitasking in JavaScript without freezing your UI.