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JavaScript Arrays - GeeksforGeeks

Last Updated : 07 Jun, 2025

In JavaScript, an array is an ordered list of values. Each value is called an element, and each element has a numeric position in the array, known as its index. Arrays in JavaScript are zero-indexed, meaning the first element is at index 0, the second at index 1, and so on.

If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:

let car1 = "Saab"
let car2 = "Volvo"
let car3 ="BMW"

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?

The solution is an array!

An array can hold many values under a single name, and you can access the values by referring to an index number.

Creating an array using array literal involves using square brackets [] to define and initialize the array.

// Creating an Empty Array
let a = [];
console.log(a);

// Creating an Array and Initializing with Values
let b = [10, 20, 30];
console.log(b);

The "Array Constructor" refers to a method of creating arrays by invoking the Array constructor function.

// Creating and Initializing an array with values
let a = new Array(10, 20, 30);

console.log(a);

Note: Both the above methods do exactly the same. Use the array literal method for efficiency, readability, and speed.

Recommended Links

• Insert Elements in a JS array
• Delete Elements from a JS Array
• Interesting Facts about JavaScript Arrays
• JavaScript Array Reference
• JavaScript Array Examples
• Cheat Sheet-A Basic guide to JavaScript.

Any element in the array can be accessed using the index number. The index in the arrays starts with 0.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"];

// Accessing Array Elements
console.log(a[0]);
console.log(a[1]);

The array indexing starts from 0, so we can access first element of array using the index number.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"];

// Accessing First Array Elements
let fst = a[0];

console.log("First Item: ", fst);

We can access the last array element using [array.length - 1] index number.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"];

// Accessing Last Array Elements
let lst = a[a.length - 1];

console.log("First Item: ", lst);

Elements in an array can be modified by assigning a new value to their corresponding index.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"];
console.log(a);

a[1]= "Bootstrap";
console.log(a);

[ 'HTML', 'CSS', 'JS' ]
[ 'HTML', 'Bootstrap', 'JS' ]

Elements can be added to the array using methods like push() and unshift().

• The push() method add the element to the end of the array.
• The unshift() method add the element to the starting of the array.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"];

// Add Element to the end of Array
a.push("Node.js");

// Add Element to the beginning
a.unshift("Web Development");

console.log(a);

[ 'Web Development', 'HTML', 'CSS', 'JS', 'Node.js' ]

To remove the elements from an array we have different methods like pop(), shift(), or splice().

• The pop() method removes an element from the last index of the array.
• The shift() method removes the element from the first index of the array.
• The splice() method removes or replaces the element from the array.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"];
console.log("Original Array: " + a);

// Removes and returns the last element
let lst = a.pop();
console.log("After Removing the last: " + a);

// Removes and returns the first element
let fst = a.shift();
console.log("After Removing the First: " + a);

// Removes 2 elements starting from index 1
a.splice(1, 2);
console.log("After Removing 2 elements starting from index 1: " + a);

Original Array: HTML,CSS,JS
After Removing the last: HTML,CSS
After Removing the First: CSS
After Removing 2 elements starting from index 1: CSS

We can get the length of the array using the array length property.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"];

let len = a.length;

console.log("Array Length: " + len);

We can increase and decrease the array length using the JavaScript length property.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"]

// Increase the array length to 7
a.length = 7;

console.log("After Increasing Length: ", a);

// Decrease the array length to 2
a.length = 2;
console.log("After Decreasing Length: ", a)

After Increasing Length:  [ 'HTML', 'CSS', 'JS', <4 empty items> ]
After Decreasing Length:  [ 'HTML', 'CSS' ]

We can iterate array and access array elements using for loop and forEach loop.

Example: It is an example of for loop.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"];

// Iterating through for loop
for (let i = 0; i < a.length; i++) {
    console.log(a[i])
}

Example: It is the example of Array.forEach() loop.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"];

// Iterating through forEach loop
a.forEach(function myfunc(x) {
    console.log(x);
});

Combine two or more arrays using the concat() method. It returns new array containing joined arrays elements.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS", "React"];
let b = ["Node.js", "Expess.js"];

// Concatenate both arrays
let concateArray = a.concat(b);

console.log("Concatenated Array: ", concateArray);

Concatenated Array:  [ 'HTML', 'CSS', 'JS', 'React', 'Node.js', 'Expess.js' ]

We have a builtin method toString() to converts an array to a string.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"];

// Convert array ot String
console.log(a.toString());

The JavaScript typeof operator is used ot check the type of an array. It returns "object" for arrays.

// Creating an Array and Initializing with Values
let a = ["HTML", "CSS", "JS"];

// Check type of array
console.log(typeof a);

There are two methods by which we can recognize a JavaScript array:

• By using Array.isArray() method
• By using instanceof method 

Below is an example showing both approaches:

const courses = ["HTML", "CSS", "Javascript"];
console.log("Using Array.isArray() method: ", Array.isArray(courses))
console.log("Using instanceof method: ", courses instanceof Array)

Using Array.isArray() method:  true
Using instanceof method:  true

Note: A common error is faced while writing the arrays:

const a = [5]
// and
const a = new Array(5) 

The above two statements are not the same.

Output: This statement creates an array with an element " [5] ". Try with the following examples

// Example 1
const a1 = [5]
console.log(a1)

// Example 2
const a2 = new Array(5) 
console.log(a2)

[ 5 ]
[ <5 empty items> ]

Apart from these get the complete list of Array Methods by following the Article - JavaScript Array Methods

• Print Alternates
• Linear Search
• Largest Element
• Second Largest
• Remove Duplicates from Sorted
• Generate all Subarrays
• Reverse an Array
• Rotate an Array

• Largest Element in an Array in Javascript
• Second Largest Element in Array
• Check if array is sorted in Javascript
• Reverse an Array in Javascript
• Move all zeros to end in Javascript
• Left Rotate by One in an Array in JavaScript
• Leaders in an Array in JS
• Frequencies in a Sorted array in JS

• Sort an array of 1 to n
• Reorder according to given indexes
• Minimum Swaps to Sort
• Sort an array of 0s, 1s and 2s
• Merge with O(1) extra space
• Majority Element

• 4 Sum - Distinct Quadruples
• 4 Sum - All Quadruples
• 4 Sum - Closest Quadruple
• Surpasser Count
• Top K Frequent Elements in an Array
• Kth Missing Positive Number in a Sorted Array

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