Callbag Basics Save

👜 Tiny and fast reactive/iterable programming library

Project README

Callbag basics 👜

Basic callbag factories and operators to get started with. Callbag is just a spec, but callbag-basics is a real library you can use.


  • Supports reactive stream programming
  • Supports iterable programming (also!)
  • Same operator works for both of the above
  • Tiny! Weighs just 7kB
  • Fast! Faster than xstream and RxJS
  • Extensible: no core library! Everything is a utility function

Imagine a hybrid between an Observable and an (Async)Iterable, that's what callbags are all about. In addition, the internals are tiny because it's all done with a few simple callbacks, following the callbag spec. As a result, it's tiny and fast.


npm install callbag-basics

Import operators and factories:

const {forEach, fromIter, map, filter, pipe} = require('callbag-basics');

Try it online

Reactive programming examples

Log XY coordinates of click events on <button> elements:

const {forEach, fromEvent, map, filter, pipe} = require('callbag-basics');

  fromEvent(document, 'click'),
  filter(ev => === 'BUTTON'),
  map(ev => ({x: ev.clientX, y: ev.clientY})),
  forEach(coords => console.log(coords))

// {x: 110, y: 581}
// {x: 295, y: 1128}
// ...

Pick the first 5 odd numbers from a clock that ticks every second, then start observing them:

const {forEach, interval, map, filter, take, pipe} = require('callbag-basics');

  map(x => x + 1),
  filter(x => x % 2),
  forEach(x => console.log(x))

// 1
// 3
// 5
// 7
// 9

Iterable programming examples

From a range of numbers, pick 5 of them and divide them by 4, then start pulling those one by one:

const {forEach, fromIter, take, map, pipe} = require('callbag-basics');

function* range(from, to) {
  let i = from;
  while (i <= to) {
    yield i;

  fromIter(range(40, 99)), // 40, 41, 42, 43, 44, 45, 46, ...
  take(5), // 40, 41, 42, 43, 44
  map(x => x / 4), // 10, 10.25, 10.5, 10.75, 11
  forEach(x => console.log(x))

// 10
// 10.25
// 10.5
// 10.75
// 11


The list below shows what's included.

Source factories

Sink factories

Transformation operators

Filtering operators

Combination operators




  • source: a callbag that delivers data
  • sink: a callbag that receives data
  • puller sink: a sink that actively requests data from the source
  • pullable source: a source that delivers data only on demand (on receiving a request)
  • listener sink: a sink that passively receives data from the source
  • listenable source: source which sends data to the sink without waiting for requests
  • operator: a callbag based on another callbag which applies some operation


The Callbag philosophy is: build it yourself. :) You can send pull requests, but even better, don't depend on the repo owner accepting it. Just fork the project, customize it as you wish, and publish your fork on npm. As long as it follows the callbag spec, everything will be interoperable! :)

Open Source Agenda is not affiliated with "Callbag Basics" Project. README Source: staltz/callbag-basics
Open Issues
Last Commit
7 months ago

Open Source Agenda Badge

Open Source Agenda Rating