Web Workers vs Service Workers — When to Use What?
Modern web applications demand performance and resilience. Two browser technologies — Web Workers and Service Workers — enable background processing and offline capabilities, but they serve fundamentally different purposes.
Core Difference
| Feature | Web Workers | Service Workers |
|---|---|---|
| Primary Purpose | Heavy computation | Network control & offline caching |
| Runs When? | Only when app is open | Even when app is closed |
| Use Cases | CPU tasks, JSON parsing | Offline, caching, push notifications |
When to Use Web Workers
Use Web Workers when the UI must remain responsive during heavy computation.
- Data processing
- Image/audio manipulation
- Large-file parsing
- Mathematical computations
const worker = new Worker("worker.js");
worker.postMessage(data);
worker.onmessage = (e) => console.log(e.data);When to Use Service Workers
Service Workers function as a proxy layer between browser and network, ideal for offline-first apps.
- Caching & Asset Management
- Background Sync
- Push Notifications
- Retry Mechanisms
self.addEventListener("fetch", (event) => {
event.respondWith(
caches.match(event.request).then(r => r || fetch(event.request))
);
});Web Workers improve computation performance.
Service Workers improve application resilience.
Scalable systems often use both.