JavaScript modules in workers
Module workers let Web Workers use standard ES module imports and exports. They make worker code easier to structure, share, and maintain than older script-style worker setups.
Overview
Module workers let Web Workers use standard ES module imports and exports. They make worker code easier to structure, share, and maintain than older script-style worker setups.
Browser support
| Feature | Desktop | Mobile | ||||
|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Safari | Chrome Android | Safari iOS | |
api.Worker.Worker.ecmascript_modules | 80 | 80 | 114 | 15 | 80 | 15 |
| DOM API | ||||||
Worker (options type parameter) `options.type` parameter | 80 | 80 | 114 | 15 | 80 | 15 |
| Operator | ||||||
worker support Available in workers | 80 | 80 | 114 | 15 | 80 | 15 |
| Statement | ||||||
worker support Available in workers | 80 | 80 | 114 | 15 | 80 | 15 |
1+Supported (version) Not supported ※Has note Sub-feature descriptions sourced from MDN Web Docs (CC BY-SA 2.5)
Notes 2 item(s)
Implementation note
- Nested workers support was introduced in Safari 15.5.
- Script loading in nested workers was introduced in Safari 16.4.
Notes 2 item(s)
Implementation note
- Nested workers support was introduced in Safari on iOS 15.5.
- Script loading in nested workers was introduced in Safari on iOS 16.4.
Syntax
JAVASCRIPT
const worker = new Worker('worker.js', { type: 'module' });
// Inside worker.js
import { process } from './utils.js';
process(data);Use cases
Shared worker utilities
Import parsing, math, or formatting helpers directly into worker code instead of bundling everything into one file.
Heavy background tasks
Keep CPU-intensive work off the main thread while preserving a clean module structure.
Cautions
- Worker execution still has different global APIs and loading constraints from the main thread, even when modules are supported.
- Check bundling and deployment paths carefully because worker URLs and module resolution must still line up.
Accessibility
- Moving work into a worker can improve responsiveness, which directly helps keyboard and assistive technology users.
- Performance gains do not replace the need for clear loading states when background work affects visible UI.
Related links
Powered by web-features