web-worker

Native cross-platform Web Workers. Works in published npm modules.

**In Node**, it's a web-compatible Worker implementation atop Node's [worker_threads](https://nodejs.org/api/worker_threads.html). **In the browser** (and when bundled for the browser), it's simply an alias of `Worker`. ### Features _Here's how this is different from worker_threads:_ - makes Worker code compatible across browser and Node - supports Module Workers (`{type:'module'}`) natively in Node 12.8+ - uses DOM-style events (`Event.data`, `Event.type`, etc) - supports event handler properties (`worker.onmessage=..`) - `Worker()` accepts a module URL, Blob URL or Data URL - emulates browser-style [WorkerGlobalScope] within the worker ### Usage Example In its simplest form: ```js import Worker from 'web-worker'; const worker = new Worker('data:,postMessage("hello")'); worker.onmessage = e => console.log(e.data); // "hello" ```

main.js	worker.js
```js import Worker from 'web-worker'; const url = new URL('./worker.js', import.meta.url); const worker = new Worker(url); worker.addEventListener('message', e => { console.log(e.data) // "hiya!" }); worker.postMessage('hello'); ```	```js addEventListener('message', e => { if (e.data === 'hello') { postMessage('hiya!'); } }); ```

👉 Notice how `new URL('./worker.js', import.meta.url)` is used above to load the worker relative to the current module instead of the application base URL. Without this, Worker URLs are relative to a document's URL, which in Node.js is interpreted to be `process.cwd()`. > _Support for this pattern in build tools and test frameworks is still limited. We are [working on growing this](https://github.com/developit/web-worker/issues/4)._ ### Module Workers Module Workers are supported in Node 12.8+ using this plugin, leveraging Node's native ES Modules support. In the browser, they can be used natively in Chrome 80+, or in all browsers via [worker-plugin] or [rollup-plugin-off-main-thread]. As with classic workers, there is no difference in usage between Node and the browser:

main.mjs	worker.mjs
```js import Worker from 'web-worker'; const worker = new Worker( new URL('./worker.mjs', import.meta.url), { type: 'module' } ); worker.addEventListener('message', e => { console.log(e.data) // "200 OK" }); worker.postMessage('https://httpstat.us/200'); ```	```js import fetch from 'isomorphic-fetch'; addEventListener('message', async e => { const url = e.data; const res = await fetch(url) const text = await res.text(); postMessage(text); }); ```

### Data URLs Instantiating Worker using a Data URL is supported in both module and classic workers: ```js import Worker from 'web-worker'; const worker = new Worker(`data:application/javascript,postMessage(42)`); worker.addEventListener('message', e => { console.log(e.data) // 42 }); ``` ### Special Thanks This module aims to provide a simple and forgettable piece of infrastructure, and as such it needed an obvious and descriptive name. [@calvinmetcalf](https://github.com/calvinmetcalf), who you may recognize as the author of [Lie](https://github.com/calvinmetcalf/lie) and other fine modules, gratiously offered up the name from his `web-worker` package. Thanks Calvin! [worker-plugin]: https://github.com/googlechromelabs/worker-plugin [rollup-plugin-off-main-thread]: https://github.com/surma/rollup-plugin-off-main-thread [WorkerGlobalScope]: https://developer.mozilla.org/en-US/docs/Web/API/WorkerGlobalScope