How to append something to an array?

Answer 1

If you know the highest index (such as stored in a variable "i") then you can do

myArray[i + 1] = someValue;

However if you don't know then you can either use

myArray.push(someValue);

as other answers suggested, or you can use

myArray[myArray.length] = someValue; 

Note that the array is zero based so .length return the highest index plus one.

Also note that you don't have to add in order and you can actually skip values, as in

myArray[myArray.length + 1000] = someValue;

In which case the values in between will have a value of undefined.

It is therefore a good practice when looping through a JavaScript to verify that a value actually exists at that point.

This can be done by something like the following:

if(myArray[i] === "undefined"){ continue; }

if you are certain that you don't have any zeros in the array then you can just do:

if(!myArray[i]){ continue; }

Of course make sure in this case that you don't use as the condition myArray[i] (as some people over the internet suggest based on the end that as soon as i is greater then the highest index it will return undefined which evaluates to false)

Answer 2

Append a single item

To append a single item to an array, use the push() method provided by the Array object:

const fruits = ['banana', 'pear', 'apple']
fruits.push('mango')
console.log(fruits)

push() mutates the original array.

To create a new array instead, use the concat() Array method:

const fruits = ['banana', 'pear', 'apple']
const allfruits = fruits.concat('mango')
console.log(allfruits)

Notice that concat() does not actually add an item to the array, but creates a new array, which you can assign to another variable, or reassign to the original array (declaring it as let, as you cannot reassign a const):

const fruits = ['banana', 'pear', 'apple']
const allfruits = fruits.concat('mango')
console.log(allfruits)

let fruits = ['banana', 'pear', 'apple']
fruits = fruits.concat('mango')

Append multiple items

To append a multiple item to an array, you can use push() by calling it with multiple arguments:

const fruits = ['banana', 'pear', 'apple']
fruits.push('mango', 'melon', 'avocado')
console.log(fruits)

You can also use the concat() method you saw before, passing a list of items separated by a comma:

const fruits = ['banana', 'pear', 'apple']
const allfruits = fruits.concat('mango', 'melon', 'avocado')
console.log(allfruits)

or an array:

const fruits = ['banana', 'pear', 'apple']
const allfruits = fruits.concat(['mango', 'melon', 'avocado'])
console.log(allfruits)

Remember that as described previously this method does not mutate the original array, but it returns a new array.

Originally posted at

Answer 3

Now, you can take advantage of ES6 syntax and just do:

let array = [1, 2];
console.log([...array, 3]);

keeping the original array immutable.

Answer 4

If you want to append a single value into an array, simply use the push method. It will add a new element at the end of the array.

But if you intend to add multiple elements then store the elements in a new array and concat the second array with the first array...either way you wish.

arr=['a','b','c'];
arr.push('d');
//now print the array in console.log and it will contain 'a','b','c','d' as elements.
console.log(array);

Answer 5

There are a couple of ways to append an array in JavaScript:

1) 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);

Output:

[1, 2, 3, 4, 5]

2) The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array:

var a = [1, 2, 3];
a.unshift(4, 5);
console.log(a); 

Output:

[4, 5, 1, 2, 3]

3) The concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.

var arr1 = ["a", "b", "c"];
var arr2 = ["d", "e", "f"];
var arr3 = arr1.concat(arr2);
console.log(arr3);

Output:

[ "a", "b", "c", "d", "e", "f" ]

4) You can use the array's .length property to add an element to the end of the array:

var ar = ['one', 'two', 'three'];
ar[ar.length] = 'four';
console.log( ar ); 

Output:

 ["one", "two", "three", "four"]

5) The splice() method changes the content of an array by removing existing elements and/or adding new elements:

var myFish = ["angel", "clown", "mandarin", "surgeon"];
myFish.splice(4, 0, "nemo");
//array.splice(start, deleteCount, item1, item2, ...)
console.log(myFish);

Output:

["angel", "clown", "mandarin", "surgeon","nemo"]

6) You can also add a new element to an array simply by specifying a new index and assigning a value:

var ar = ['one', 'two', 'three'];
ar[3] = 'four'; // add new element to ar
console.log(ar);

Output:

["one", "two","three","four"]

Answer 6

Let the array length property do the work:

myarray[myarray.length] = 'new element value added to the end of the array';

myarray.length returns the number of strings in the array. JS is zero based so the next element key of the array will be the current length of the array. EX:

var myarray = [0, 1, 2, 3],
    myarrayLength = myarray.length; //myarrayLength is set to 4