This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

The Object.observe() method is used for asynchronously observing the changes to an object. It provides a stream of changes in the order in which they occur.


Object.observe(obj, callback[, acceptList])


The object to be observed.
The function called each time changes are made, with the following argument:
An array of objects each representing a change. The properties of these change objects are:
  • name: The name of the property which was changed.
  • object: The changed object after the change was made.
  • type: A string indicating the type of change taking place. One of "add", "update", or "delete".
  • oldValue: Only for "update" and "delete" types. The value before the change.
The list of types of changes to be observed on the given object for the given callback. If omitted, the array ["add", "update", "delete", "reconfigure", "setPrototype", "preventExtensions"] will be used.


callback is called each time a change is made to obj, with an array of all changes in the order in which they occurred.


Logging all six different types

var obj = {
  foo: 0,
  bar: 1

Object.observe(obj, function(changes) {

obj.baz = 2;
// [{name: 'baz', object: <obj>, type: 'add'}] = 'hello';
// [{name: 'foo', object: <obj>, type: 'update', oldValue: 0}]

delete obj.baz;
// [{name: 'baz', object: <obj>, type: 'delete', oldValue: 2}]

Object.defineProperty(obj, 'foo', {writable: false});
// [{name: 'foo', object: <obj>, type: 'reconfigure'}]

Object.setPrototypeOf(obj, {});
// [{name: '__proto__', object: <obj>, type: 'setPrototype', oldValue: <prototype>}]

// [
//   {name: 'foo', object: <obj>, type: 'reconfigure'},
//   {name: 'bar', object: <obj>, type: 'reconfigure'},
//   {object: <obj>, type: 'preventExtensions'}
// ]

Data Binding

// A user model
var user = {
  id: 0,
  name: 'Brendan Eich',
  title: 'Mr.'

// Create a greeting for the user
function updateGreeting() {
  user.greeting = 'Hello, ' + user.title + ' ' + + '!';

Object.observe(user, function(changes) {
  changes.forEach(function(change) {
    // Any time name or title change, update the greeting
    if ( === 'name' || === 'title') {

Custom change type

// A point on a 2D plane
var point = {x: 0, y: 0, distance: 0};

function setPosition(pt, x, y) {
  // Performing a custom change
  Object.getNotifier(pt).performChange('reposition', function() {
    var oldDistance = pt.distance;
    pt.x = x;
    pt.y = y;
    pt.distance = Math.sqrt(x * x + y * y);
    return {oldDistance: oldDistance};

Object.observe(point, function(changes) {
  console.log('Distance change: ' + (point.distance - changes[0].oldDistance));
}, ['reposition']);

setPosition(point, 3, 4);
// Distance change: 5


Strawman proposal specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 36 Not supported [1] Not supported [2] 23 Not supported
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support Not supported 36 Not supported [1] Not supported [2] 23 Not supported

[1]: See bug 800355

[2]: See relevant MS Edge platform status entry

See also

Document Tags and Contributors

 Last updated by: fscholz,