Array.observe()

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.

Syntax

Array.observe(arr, callback)

Parameters

arr

The array 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 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.

Description

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.

Examples

Logging different change types

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

Array.observe(arr, function(changes) {
  console.log(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}]

Specifications

Strawman proposal specification.

Browser compatibility

See also

• Under what condition would Array.observe's “add” event trigger?
• Array.unobserve()
• Object.observe()