Javascript Array

Introduction

In JavaScript, an array is a special type of object used to store multiple values in a single variable. Arrays are ordered collections, meaning the values (called elements) are stored in a sequence, and each element can be accessed by its numerical index.

OR

An array is used to store more than one value in a single variable.

What is a JavaScript Array?

A JavaScript Array is a special variable used to store multiple values in a single variable.

Syntax of JavaScript Array

Basic syntax:

let arrayName = [value1,value2,value3];

Example:

let cities =["Delhi","Mumbai","Noida"];

Why JavaScript Arrays are Used?

There are many reasons to use JavaScript Arrays

• Store Multiple Values
• Easy Data Management
• Loop Through Data
• Useful in APIs
• Required in Modern JavaScript

Creating Arrays in JavaScript

There are many ways to create an array in JavaScript.

Method 1: Using Square Brackets

This is the most common method to create a Array.

let fruits = ["Apple","Banana","Mango"];

Method 2: Using Array Constructor

let colors = new Array("Red","Blue","Green");

Method 3: Empty Array

let users = [];
// now you can add name through push method
users.push("John");

Accessing Array Elements

Arrays use indexes to store values, and the index starts at 0.

Example:

let fruits = ["Apple","Banana","Mango"];
console.log(fruits[0]);

Output:

Access the second element:

let fruits = ["Apple","Banana","Mango"];
console.log(fruits[1]);

Output:

Updating Array Values

Suppose you have to update the value from Red to Black.

let colors = ["Red","Blue"];
colors[0]="Black";
console.log(colors);

Output:

Finding Array Length

to get the array length through the method below

Syntax:

arrayName.length

Example:

let fruits = ["Apple","Banana","Mango"];
console.log(fruits.length);

Output:

JavaScript Array Methods

You will see some JavaScript Array methods that are most important for the project development.

1. push()

This method is used to add an element to the end of the Array element.

users=["John","Tom"];
users.push("Rom");
console.log(users);

Output:

2. pop()

This method removes the last element.

users=["John","Tom"];
users.pop("Rom");
console.log(users);

Output:

3. shift()

This method removes the first element.

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

Output:

4. unshift()

This method is used to add at the beginning.

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

Output:

5. includes()

This method is used to check whether the value exists or not.

let fruits = ["Apple","Banana"];
console.log(fruits.includes("Apple"));

Output:

6. indexOf()

This method is used to find the position.

let fruits = ["Apple","Banana"];
console.log(fruits.indexOf("Banana"));

Output:

7. slice()

This method is used to extract part of an array.

let nums = [1,2,3,4];
console.log(nums.slice(1,3));

Output:

8. splice()

This method is used to add/remove elements.

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

Output:

Explanation:

• 1 (startIndex) → Start at index 1 (value 2)
• 1 (deleteCount) → Remove 1 element

Using for Loop Through Arrays

let fruits = ["Apple","Banana"];

for(let i=0; i<fruits.length; i++)
{
console.log(fruits[i]);
}

Output:

Multidimensional Arrays

Array inside array.

let data = [
["John",35],
["Tom",30]
];
console.log(data[0][0]);

Output:

Real-Life Example 1: Todo List

let todos = ["Study","Exercise","Coding"];

todos.push("Sleep");
console.log(todos);

Output:

Real-Life Example 2: Get the total Marks of Student

let marks = [90,85,70];
let total = marks[0] + marks[1] + marks[2];
console.log(total);

Output:

Common Mistakes in Arrays

Mistake 1: Access Wrong Index

Wrong:

let arr=[1,2];
console.log(arr[5]);

Output:

Mistake 2: Using () Instead of []

Wrong:

arr(0)

Correct:

arr[0]

Difference Between Array and Object

Feature	Array	Object
Storage	Multiple values	Key-value pairs
Index	Numeric	Named keys
Syntax	[]	{}
Example	["HTML","CSS"]	{   name: "John" }

JavaScript Array – Interview Questions

JavaScript Array – Objective Questions (MCQs)

Conclusion

JavaScript arrays are essential for storing and managing multiple values efficiently. They simplify data handling, improve code readability, and are widely used in web applications, APIs, and frameworks.

Understanding arrays and methods like push(), pop(), slice(), and splice() helps build stronger JavaScript fundamentals.