This is an archived page. It's not actively maintained.


This feature is obsolete.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 Array.observe() method was used for asynchronously observing changes to Arrays, similar to Object.observe() for objects. It provided a stream of changes in order of occurrence. It's equivalent to Object.observe() invoked with the accept type list ["add", "update", "delete", "splice"]. However, this API has been deprecated and removed from Browsers. You can use the more general Proxy object instead.


Array.observe(arr, callback)


The array 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 array after the change was made.
  • type: A string indicating the type of change taking place. One of "add", "update", "delete", or "splice".
  • oldValue: Only for "update" and "delete" types. The value before the change.
  • index: Only for the "splice" type. The index at which the change occurred.
  • removed: Only for the "splice" type. An array of the removed elements.
  • addedCount: Only for the "splice" type. The number of elements added.


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

Changes done via Array methods, such as Array.prototype.pop() will be reported as "splice" changes. Index assignment changes which do not change the length of the array may be reported as "update" changes.


Logging different change types

var arr = ['a', 'b', 'c'];

Array.observe(arr, function(changes) {

arr[1] = 'B';
// [{type: 'update', object: <arr>, name: '1', oldValue: 'b'}]

arr[3] = 'd';
// [{type: 'splice', object: <arr>, index: 3, removed: [], addedCount: 1}]

arr.splice(1, 2, 'beta', 'gamma', 'delta');
// [{type: 'splice', object: <arr>, index: 1, removed: ['B', 'c'], addedCount: 3}]


Strawman proposal specification.

Browser compatibility

Supported nowhere. Historically supported in Chrome 36 till 52.

See also