Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

https://github.com/developit/greenlet

🦎 Move an async function into its own thread.
https://github.com/developit/greenlet

thread web-worker webworker worker workerize

Last synced: 18 days ago
JSON representation

🦎 Move an async function into its own thread.

Lists

README 

        


  Greenlet




## Greenlet [![npm](https://img.shields.io/npm/v/greenlet.svg)](https://npm.im/greenlet) [![travis](https://travis-ci.org/developit/greenlet.svg?branch=master)](https://travis-ci.org/developit/greenlet) [![gzip size](http://img.badgesize.io/https://unpkg.com/greenlet/dist/greenlet.js?compression=gzip)](https://unpkg.com/greenlet/dist/greenlet.umd.js) [![install size](https://packagephobia.now.sh/badge?p=greenlet)](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)