How to add elements to an existing array dynamically in JavaScript ?

An array is a JavaScript object that can hold multiple values at a time, irrespective of the data type.

Example:

var a = ['Geeks', 'For', 'Geeks', 1];

In the above example, “Geeks” is of type “string” while 1 is of “integer” type. An array can also store JavaScript objects. JavaScript arrays are dynamic in nature, they do not need the size during initialization. They are accessed using numbered indexes.

console.log(a[1]);

Above statement prints ‘For’ from the above example in the console window.

Output:

For

or

document.write(a[1]);

Output:

For

To add elements into an array dynamically in JavaScript, the programmer can use any of the following methods.

Method 1: Use number indexes to add an element to the specified index.

JavaScript

<script>
    // JavaScript Array Initialization
    var a = ['Hi', 'There'];

    // New element added dynamically.
    a[3] = 'Geeks';

    document.write(a[3]);
    document.write("<br>");
    document.write(a[2]);
</script>

Output: On the console window

It can be seen that index of {0, 1} was declared only. Index 3 was dynamically created and initialized to ‘Geeks’. Index 2 was created automatically and initialized to undefined, to keep up the ordering.

Method 2: Use push() method is used to add element at the end of the array.

JavaScript

<script>
    // JavaScript Array Declared
    var a = [];

    // Elements pushed into the
    // array using push() method
    a.push('Geeks');
    a.push('For');
    a.push('Geeks');

    // Obtaining the value
    document.write(a);
</script>

Output:

The console window shows an array object containing 3 values, they are [‘Geeks’, ‘For’, ‘Geeks’]. The push() method maintains the ordering of indexes by adding the new elements at the end of the array and returns the new length of the array.