Push string to object javascript

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Syntax

push(element0)
push(element0, element1)
push(element0, element1, /* … ,*/ elementN)

Parameters

elementN

The element(s) 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.

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

The push() method is a mutating method. It changes the length and the content of this. In case you want the value of this to be the same, but return a new array with elements appended to the end, you can use arr.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 of concat().

Array.prototype.push() is intentionally generic. This method can be called 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.

Although strings are native Array-like objects, 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.

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

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

Merging two arrays

This example uses spread syntax to push all elements from a second array into the first one.

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

// Merge the second array into the first one
vegetables.push(...moreVegs);

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

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

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 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 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.

See also