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Obsolete
This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.

The Object.observe() method was used for asynchronously observing the changes to an object. It provided a stream of changes in the order in which they occur. However, this API has been deprecated and removed from browsers. You can use the more general Proxy object instead.

Syntax

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

Parameters

obj
The object to be observed.
callback
The function called each time changes are made, with the following argument:
changes
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.
acceptList
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.

Return value

The object to be observed.

Description

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

Examples

Logging all six different types

var obj = {
  foo: 0,
  bar: 1
};

Object.observe(obj, function(changes) {
  console.log(changes);
});

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

obj.foo = '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>}]

Object.seal(obj);
// [
//   {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 + ' ' + user.name + '!';
}
updateGreeting();

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

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

Specifications

Strawman proposal specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 36 [1] No support [2] No support [3] 23 No support
Feature Android Android Webview Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support No support (Yes) [1] No support [2] No support [3] 23 No support 36[1]

[1] Deprecated in Chrome 49 and flagged off in Chrome 50 and entirely removed in Chrome 52

[2] See bug 800355

[3] See relevant MS Edge platform status entry

See also

Document Tags and Contributors

 Last updated by: eduardoboucas,