element1, …,elementN

The element(s) to add to the end of the array.

The newlength property of the object upon which the method was called.

Thepush() method appends values to an array.

Array.prototype.unshift() has similar behavior topush(), but applied to the start of an array.

Thepush() method is amutating method. It changes the length and the content ofthis. In case you want the value ofthis to be the same, but return a new array with elements appended to the end, you can usearr.concat([element0, element1, /* ... ,*/ elementN]) instead. Notice that the elements are wrapped in an extra array — otherwise, if the element is an array itself, it would be spread instead of pushed as a single element due to the behavior ofconcat().

Thepush() method isgeneric. It only expects thethis value to have alength property and integer-keyed properties. Although strings are also array-like, this method is not suitable to be applied on them, as strings are immutable.

The following code creates thesports array containing two elements, thenappends two elements to it. Thetotal variable contains the new length ofthe array.

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

This example usesspread syntax to push all elements from asecond array into the first one.

const vegetables = ["parsnip", "potato"];const moreVegs = ["celery", "beetroot"];// Merge the second array into the first onevegetables.push(...moreVegs);console.log(vegetables); // ['parsnip', 'potato', 'celery', 'beetroot']

Merging two arrays can also be done with theconcat() method.

Thepush() method reads thelength property ofthis. It then sets each index ofthis starting atlength with the arguments passed topush(). Finally, it sets thelength to the previous length plus the number of pushed elements.

const arrayLike = {  length: 3,  unrelated: "foo",  2: 4,};Array.prototype.push.call(arrayLike, 1, 2);console.log(arrayLike);// { '2': 4, '3': 1, '4': 2, length: 5, unrelated: 'foo' }const plainObj = {};// There's no length property, so the length is 0Array.prototype.push.call(plainObj, 1, 2);console.log(plainObj);// { '0': 1, '1': 2, length: 2 }

As mentioned above,push is intentionally generic, and we can use that toour advantage.Array.prototype.push can work on an object just fine, asthis example shows.

Note that we don't create an array to store a collection of objects. Instead, we storethe collection on the object itself and usecall onArray.prototype.push to trick the method into thinking we are dealing withan array—and it just works, thanks to the way JavaScript allows us to establish theexecution context in any way we want.

const obj = {  length: 0,  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 althoughobj is not an array, the methodpushsuccessfully incrementedobj'slength property just like if wewere dealing with an actual array.

• Polyfill ofArray.prototype.push incore-js with fixes of this method
• es-shims polyfill ofArray.prototype.push
• Indexed collections guide
• Array
• Array.prototype.pop()
• Array.prototype.shift()
• Array.prototype.unshift()
• Array.prototype.concat()
• Array.prototype.splice()