Awesome Open Source
Awesome Open Source


A smart and efficient javascript object observer, ideal for batching DOM updates (~1kb)

Build Status NPM version NPM downloads MIT License


Via npm

$ npm i icaro -S

Script import

Via <script>

<script src='path/to/icaro.js'></script>

Via ES2015 modules

import icaro from 'icaro'

Via commonjs

const icaro = require('icaro')



icaro is really fast compared to the other reactive libs because it smartly throttles all the state changes.


icaro will let you listen to all the changes happening in a javascript object or array, grouping them efficiently, and optimizing the performance of your listeners.

const obj = icaro({})

// the variable "changes" here is a Map and the function is async
obj.listen(function(changes) {
  console.log(changes.get('foo')) // 'hi'
  console.log(changes.get('bar')) // 'there'
  console.log(changes.get('baz')) // 'dude'

  // kill all the listeners
}) = 'hi' = 'there'
obj.baz = 'dude'

icaro will also let you listen to nested objects and all the non primitive properties added to an icaro object will be automatically converted into icaro observable objects.

const obj = icaro({})

// listen only the changes happening on the root object
obj.listen(function(changes) {

obj.nested = {


obj.nested.listen(function(changes) {
  // listen only the changes of obj.nested

obj.nested.someVal = 'hello'

icaro is able also to listen changes in arrays. Any change to the items indexes will dispatch events.

// Here a bit of hardcore async stuff

const arr = icaro([])

// here you will get the index of the items added or who changed their position
arr.listen(function(changes) {
  console.log(changes.get('0')) // 'foo'
  console.log(changes.get('1')) // 'bar'
  // kill all the listeners this included

  // add a brand new listener recursively.. why not?
  arr.listen(function(changes) {
    // the change was triggered by a 'reverse' and all indexes were updated
    console.log(changes.get('0')) // 'bar'
    console.log(changes.get('1')) // 'foo'

  // update all the indexes

// initial dispatch

You can also avoid unsubscribing ("unlisten") because icaro will automatically remove event listeners when the object is about to be garbage collected.


Any icaro call will return a Proxy with the following api methods


Listen any object or array calling the callback function asynchronously grouping all the contiguous changes via setImmediate

@returns self


Unsubscribing a callback previously subscribed to the object, if no callback is provided all the previous subscriptions will be cleared

@returns self


Return all data contained in an icaro Proxy as JSON object

@returns Object


icaro uses advanced es6 features like Proxies, WeakMaps, Maps and Symbols and it targets only modern browsers

All major evergreen browsers (Edge, Chrome, Safari, Firefox) should be supported

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javascript (70,969
proxy (566
observable (62
object (45