greenlet

## Greenlet [](https://npm.im/greenlet) [](https://travis-ci.org/developit/greenlet) [](https://unpkg.com/greenlet/dist/greenlet.umd.js) [](https://packagephobia.now.sh/result?p=greenlet) > Move an async function into its own thread. > > A simplified single-function version of [workerize](https://github.com/developit/workerize), offering [the same performance as direct Worker usage](https://esbench.com/bench/5b16b61af2949800a0f61ce3). The name is somewhat of a poor choice, but it was [available on npm](https://npm.im/greenlet). _Greenlet supports IE10+, since it uses [Web Workers](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Using_web_workers). For NodeJS usage, Web Workers must be polyfilled using a library like [node-webworker](https://github.com/pgriess/node-webworker)._ ## Installation & Usage ```sh npm i -S greenlet ``` Accepts an async function with, produces a copy of it that runs within a Web Worker. > ⚠️ **Caveat:** the function you pass cannot rely on its surrounding scope, since it is executed in an isolated context. ``` greenlet(Function) -> Function ``` > ‼️ **Important:** never call greenlet() dynamically. Doing so creates a new Worker thread for every call: ```diff -const BAD = () => greenlet(x => x)('bad') // creates a new thread on every call +const fn = greenlet(x => x); +const GOOD = () => fn('good'); // uses the same thread on every call ``` Since Greenlets can't rely on surrounding scope anyway, it's best to always create them at the "top" of your module. ## Example Greenlet is most effective when the work being done has relatively small inputs/outputs. One such example would be fetching a network resource when only a subset of the resulting information is needed: ```js import greenlet from 'greenlet' let getName = greenlet( async username => { let url = `https://api.github.com/users/${username}` let res = await fetch(url) let profile = await res.json() return profile.name }) console.log(await getName('developit')) ``` [ **Run this example on JSFiddle**](https://jsfiddle.net/developit/mf9fbma5/) ## Transferable ready Greenlet will even accept and optimize [transferables](https://developer.mozilla.org/en-US/docs/Web/API/Transferable) as arguments to and from a greenlet worker function. ## Browser support Thankfully, Web Workers have been around for a while and [are broadly supported](https://caniuse.com/#feat=webworkers) by Chrome, Firefox, Safari, Edge, and Internet Explorer 10+. If you still need to support older browsers, you can just check for the presence of `window.Worker`: ```js if (window.Worker) { ... } else { ... } ``` ### CSP If your app has a [Content-Security-Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy), Greenlet requires `worker-src blob:` and `script-src blob:` in your config. ## License & Credits > In addition to the contributors, credit goes to [@sgb-io](https://github.com/sgb-io) for his annotated exploration of Greenlet's source. This prompted a refactor that clarified the code and allowed for further size optimizations. [MIT License](https://oss.ninja/mit/developit)