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Like RxJS, but for normal people.

Really? Why?

The Reactive Extensions for JavaScript, or RxJS, give us a new way to think about how data flows through your application. Rather than gaffer taping your application together with listeners that respond to discrete events, Rx allows us to think about streams of values. The power of this approach becomes obvious when you manipulate and combine streams – throttling keypresses in a search field and discarding obsolete AJAX responses, for example.

On a recent project, I decided to use RxJS to avoid what would otherwise have quickly become a spaghetti mess of imperative code. But I'm not used to thinking in streams, and found myself fighting the library at every turn. The Reactive mantra that anything can be stream (from this excellent introduction) soon gave way to everything must be a stream. Figuring out how to use Reactive concepts alongside more familiar techniques was beyond me in the limited time I had available before my deadline.

So I did the only sensible thing and wrote my own library, with the following goals:

  • tiny – if you're using a modern module bundler such as Rollup or Webpack 2, any unused operators will be discarded. Like a tightly-optimised custom build, except with zero configuration
  • readable – you should be able to read the source code and understand exactly what is going on
  • easy – ideological purity may be sacrificed in the name of getting stuff done
  • familiar – operators are modelled after their RxJS counterparts. If you're familiar with flatMapLatest and distinctUntilChanged and friends, you'll know exactly what is going on

You should use Gurgle if...

  • You want to dabble with streams but can't afford to take several frustrating weeks to rewire your brain
  • You want to introduce streams into an existing codebase gradually
  • You don't want to add a hefty dependency to your app

You shouldn't use Gurgle if...

  • You need the full functionality of RxJS (right now, Gurgle is missing lots of operators and sources. You should contribute!)
  • Your app is extremely performance-sensitive (RxJS has been battle-tested at places like Netflix, whereas this... well, I wrote it in a couple of afternoons. It doesn't (yet) have concepts like schedulers and backpressure)
  • You enjoy ideological bunfights about the true nature of FRP and suchlike


npm install --save gurgle


You can import individual functions into your app using this ES6 syntax...

import { stream, map, filter } from 'gurgle';

...but for the sake of convenience, we'll do it like this in all of the examples:

import * as g from 'gurgle';

This is equivalent to var g = require('gurgle') if you're old school. (It comes with a UMD build, so you can also use it with an AMD loader or plain ol' script tags.)

Your first stream

You can create a stream of arbitrary values like so:

const stream = () => {
    // this callback is optional – if provided, will be 
    // called when the stream is closed. Use it for 
    // detaching event handlers etc 
    console.log( 'cleaning up' );
// All streams have a `push` method, which returns `this` 
stream.push( 'a' );
stream.value; // 'a' – the most recently pushed value 
// the second and third arguments to `stream.subscribe` 
// are optional. If a value has been pushed to the stream 
// the stream is considered to have 'started', and the 
// callback will be called with the current stream value 
    value => console.log( `the value is ${value}` ),
    error => console.log( `oh noes! ${error.message}` ),
    () => console.log( `closing the stream` )
// -> 'the value is a' 
stream.push( 'b' );
// -> 'the value is b' 
stream.push( 'c' ).push( 'd' ).close();
// -> 'the value is c' 
// -> 'the value is d' 
// -> 'cleaning up' 
// -> 'closing the stream' 

Once a stream is closed, you cannot push more values to it, and the subscriber functions will no longer be called.

Error handling

Calling stream.error(...) will cause any error handlers to be invoked, and will close the stream:

const anotherStream = () => {
    console.log( 'cleaning up' );
    value => console.log( `the value is ${value}` ),
    error => console.log( `oh noes! ${error.message}` ),
    () => console.log( `closing the stream` )
anotherStream.error( new Error( 'something went wrong' ) );
// -> 'oh noes! something went wrong' 
// -> 'closing the stream' 

Stream sources

Gurgle provides convenient ways to create common streams:

// fromAjax – accepts a URL and an options object. Self-closing 
const ajaxStream = g.fromAjax( '', {
    responseType: 'json'
// fromEvent – accepts a DOM node (or `window`) and 
// an event type. Removes event listener when stream 
// is closed 
const eventStream = g.fromEvent( window, 'mousemove' );
// fromPromise – creates a stream from a Promise, which 
// auto-closes once the promise resolves 
const promiseStream = g.fromPromise( doSomethingAsync() );
// fromGeolocation – watches user's location at a specified interval 
// or using watchPosition 
const geolocationStream = g.fromGeolocation({
    interval: 10 * 1e3,
    onerror ( err ) {
        // without this, geolocation errors will close the stream 
// requestAnimationFrame – creates a stream that updates every frame 
// with a tick value 
const frame = g.requestAnimationFrame();
// more to come... 


In Gurgle, operators on streams are standalone functions that return streams:

const input =;
const mapped = input, x => ... );
const filtered = g.filter( mapped, x => ... );

This works well and is inherently highly composable, but if you prefer chaining, you can do so with the pipe method:

const input =;
const filtered = input
    .pipe(, x => ... )
    .pipe( g.filter, x => ... );

Consult the wiki for details about individual operators.