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What is Array in JavaScript?

JavaScript Array is a data structure that allows you to store and organize multiple values within a single variable. It is a versatile and dynamic object. It can hold various data types, including numbers, strings, objects, and even other arrays. Arrays in JavaScript are zero-indexed i.e. the first element is accessed with an index 0, the second element with an index of 1, and so forth.

JavaScript Arrays

JavaScript Array

You can create JavaScript Arrays using the Array constructor or using the shorthand array literal syntax, which employs square brackets. Arrays can dynamically grow or shrink in size as elements are added or removed.

Basic Terminologies of JavaScript Array

  • Array: A data structure in JavaScript that allows you to store multiple values in a single variable.
  • Array Element: Each value within an array is called an element. Elements are accessed by their index.
  • Array Index: A numeric representation that indicates the position of an element in the array. JavaScript arrays are zero-indexed, meaning the first element is at index 0.
  • Array Length: The number of elements in an array. It can be retrieved using the length property.

Declaration of an Array

There are basically two ways to declare an array i.e. Array Literal and Array Constructor.

1. Creating an Array using Array Literal

Creating an array using array literal involves using square brackets [] to define and initialize the array. This method is concise and widely preferred for its simplicity.

Syntax:

let arrayName = [value1, value2, ...];

Example:

Javascript

// Creating an Empty Array
let names = [];
console.log(names);
 
// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "Javascript", "React"];
 
console.log(courses);

                    

Output
[]
[ 'HTML', 'CSS', 'Javascript', 'React' ]

2. Creating an Array using Array Constructor (JavaScript new Keyword)

The “Array Constructor” refers to a method of creating arrays by invoking the Array constructor function. This approach allows for dynamic initialization and can be used to create arrays with a specified length or elements.

Syntax:

let arrayName = new Array();

Example:

javascript

// Declaration of an empty array
// using Array constructor
let names = new Array();
console.log(names);
 
// Creating and Initializing an array with values
let courses = new Array("HTML", "CSS", "Javascript", "React");
console.log(courses);
 
// Initializing Array while declaring
let arr = new Array(3);
arr[0] = 10;
arr[1] = 20;
arr[2] = 30;
console.log(arr);

                    

Output
[]
[ 'HTML', 'CSS', 'Javascript', 'React' ]
[ 10, 20, 30 ]

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

Basic Operations on JavaScript Arrays

1. Accessing Elements of an Array

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

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "Javascript", "React"];
 
// Accessing Array Elements
console.log(courses[0]);
console.log(courses[1]);
console.log(courses[2]);
console.log(courses[3]);

                    

Output
HTML
CSS
Javascript
React

2. Accessing the First Element of an Array

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

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "JavaScript", "React"];
 
// Accessing First Array Elements
let firstItem = courses[0];
 
console.log("First Item: ", firstItem);

                    

Output
First Item:  HTML

3. Accessing the Last Element of an Array

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

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "JavaScript", "React"];
 
// Accessing Last Array Elements
let lastItem = courses[courses.length - 1];
 
console.log("First Item: ", lastItem);

                    

Output
First Item:  React

4. Modifying the Array Elements

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

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "Javascript", "React"];
console.log(courses);
 
courses[1]= "Bootstrap";
console.log(courses);

                    

Output
[ 'HTML', 'CSS', 'Javascript', 'React' ]
[ 'HTML', 'Bootstrap', 'Javascript', 'React' ]

5. Adding Elements to the Array

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

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "Javascript", "React"];
 
// Add Element to the end of Array
courses.push("Node.js");
 
// Add Element to the beginning
courses.unshift("Web Development");
 
console.log(courses);

                    

Output
[ 'Web Development', 'HTML', 'CSS', 'Javascript', 'React', 'Node.js' ]

6. Removing Elements from an Array

Remove elements using methods like pop(), shift(), or splice().

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "Javascript", "React", "Node.js"];
console.log("Original Array: " + courses);
 
// Removes and returns the last element
let lastElement = courses.pop();
console.log("After Removed the last elements: " + courses);
 
// Removes and returns the first element
let firstElement = courses.shift();
console.log("After Removed the First elements: " + courses);
 
// Removes 2 elements starting from index 1
courses.splice(1, 2);
console.log("After Removed 2 elements starting from index 1: " + courses);

                    

Output

Original Array: HTML,CSS,Javascript,React,Node.js
After Removed the last elements: HTML,CSS,Javascript,React
After Removed the First elements: CSS,Javascript,React
After Removed 2 elements starting from index 1: CSS

7. Array Length

Get the length of an array using the length property.

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "Javascript", "React", "Node.js"];
 
let len = courses.length;
 
console.log("Array Length: " + len);

                    

Output
Array Length: 5

8. Increase and Decrease the Array Length

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

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "Javascript", "React", "Node.js"];
 
// Increase the array length to 7
courses.length = 7;
 
console.log("Array After Increase the Length: ", courses);
 
// Decrease the array length to 2
courses.length = 2;
console.log("Array After Decrease the Length: ", courses)

                    

Output
Array After Increase the Length:  [ 'HTML', 'CSS', 'Javascript', 'React', 'Node.js', <2 empty items> ]
Array After Decrease the Length:  [ 'HTML', 'CSS' ]

9. Iterating Through Array Elements

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

Example: It is the example of for loop.

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "JavaScript", "React"];
 
// Iterating through for loop
for (let i = 0; i < courses.length; i++) {
    console.log(courses[i])
}

                    

Output
HTML
CSS
JavaScript
React

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

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "JavaScript", "React"];
 
// Iterating through forEach loop
courses.forEach(function myfunc(elements) {
    console.log(elements);
});

                    

Output
HTML
CSS
JavaScript
React

10. Array Concatenation

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

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "JavaScript", "React"];
let otherCourses = ["Node.js", "Expess.js"];
 
// Concatenate both arrays
let concateArray = courses.concat(otherCourses);
 
console.log("Concatenated Array: ", concateArray);

                    

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

11. Conversion of an Array to String

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

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "JavaScript", "React"];
 
// Convert array ot String
console.log(courses.toString());

                    

Output
HTML,CSS,JavaScript,React

12. Check the Type of an Arrays

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

Javascript

// Creating an Array and Initializing with Values
let courses = ["HTML", "CSS", "JavaScript", "React"];
 
// Check type of array
console.log(typeof courses);

                    

Output
object

Difference Between JavaScript Arrays and Objects

  • JavaScript arrays use indexes as numbers.
  • objects use indexes as names..

When to use JavaScript Arrays and Objects?

  • Arrays are used when we want element names to be numeric.
  • Objects are used when we want element names to be strings.

Recognizing a JavaScript Array

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

Below is an example showing both approaches:

Javascript

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

                    

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

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

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

Javascript

const numbers = [5]
console.log(numbers)

                    

The above two statements are not the same.

Output: This statement creates an array with an element ” [5] “.

[5]

Javascript

const numbers = new Array(5)
console.log(numbers)

                    

Output
[ <5 empty items> ]

JavaScript Array Complete Reference

We have a complete list of Javascript Array, to check those please go through this JavaScript Array Reference article. It contains detailed description and examples of all Array Properties and Methods.

JavaScript Array Examples

JavaScript Array examples contains list of questions that are majorily asked in interview. Please check this article JavaScript Array Examples for more detail.

JavaScript CheatSheet

We have a Cheat Sheet on Javascript where we have covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.



Last Updated : 30 Jan, 2024
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