Array.prototype.push()

The push() method adds one or more elements to the end of an array and returns the new length of the array.

var a = [1, 2, 3];
a.push(4, 5);

console.log(a); // [1, 2, 3, 4, 5]

Syntax

arr.push(element1, ..., elementN)

Parameters

elementN

The elements to add to the end of the array.

Return value

The new length property of the object upon which the method was called.

Description

The push method appends values to an array.

push is intentionally generic. This method can be used with call() or apply() on objects resembling arrays. The push method relies on a length property to determine where to start inserting the given values. If the length property cannot be converted into a number, the index used is 0. This includes the possibility of length being nonexistent, in which case length will also be created.

The only native, array-like objects are strings, although they are not suitable in applications of this method, as strings are immutable.

Examples

Adding elements to an array

The following code creates the sports array containing two elements, then appends two elements to it. The total variable contains the new length of the array.

var sports = ['soccer', 'baseball'];
var total = sports.push('football', 'swimming');

console.log(sports); // ['soccer', 'baseball', 'football', 'swimming']
console.log(total);  // 4

Merging two arrays

This example uses apply() to push all elements from a second array.

var vegetables = ['parsnip', 'potato'];
var moreVegs = ['celery', 'beetroot'];

// Merge the second array into the first one
// Equivalent to vegetables.push('celery', 'beetroot');
Array.prototype.push.apply(vegetables, moreVegs);

console.log(vegetables); // ['parsnip', 'potato', 'celery', 'beetroot']

Using an object in an array-like fashion

As mentioned above, push is intentionally generic, and we can use that to our advantage. Array.prototype.push can work on an object just fine, as this example shows. Note that we don't create an array to store a collection of objects. Instead, we store the collection on the object itself and use call on Array.prototype.push to trick the method into thinking we are dealing with an array, and it just works, thanks to the way JavaScript allows us to establish the execution context however we please.

var obj = {
    length: 0,

    addElem: function addElem (elem) {
        // obj.length is automatically incremented 
        // every time an element is added.
        [].push.call(this, elem);
    }
};

// Let's add some empty objects just to illustrate.
obj.addElem({});
obj.addElem({});
console.log(obj.length);
// → 2

Note that although obj is not an array, the method push successfully incremented obj's length property just like if we were dealing with an actual array.

Specifications

Browser compatibility

See also

• Array.prototype.pop()
• Array.prototype.shift()
• Array.prototype.unshift()
• Array.prototype.concat()