JavaScript Array indexOf() Method

The JavaScript Array indexOf() Method is used to find the index of the first occurrence of the search element provided as the argument to the method. This method always compares the search element to the element present in the array using strict equality. Therefore, when the search element is NaN then it returns -1 because NaN values are never compared as equal.

Syntax:

array.indexOf(element, start)

Parameters: This method accepts two parameters as mentioned above and described below: 

• element: This parameter holds the element whose index will be returned.
• start: This parameter is optional and it holds the starting point of the array, where to begin the search the default value is 0.

Return value: This method returns the index of the first occurrence of the element. If the element cannot be found in the array, then this method returns -1.

Example 1: Below is an example of the Array indexOf() method. 

javascript

let name = ['gfg', 'cse', 'geeks', 'portal'];
a = name.indexOf('gfg')
// Printing result of method
console.log(a)

Output

0

Example 2: In this example, the method will be searched for element 2 in that array and return that element index. 

javascript

// Taking input as an array A
// having some elements.
let A = [1, 2, 3, 4, 5];

// indexOf() method is called to
// test whether the searching element
// is present in given array or not.
a = A.indexOf(2)

// Printing result of method.
console.log(a);

Output

1

Example 3: In this example, the method will be searched for element 9 in that array if not found then return -1. 

javascript

// Taking input as an array A
// having some elements.
let name = ['gfg', 'cse', 'geeks', 'portal'];

// indexOf() method is called to
// test whether the searching element
// is present in given array or not.
a = name.indexOf('cat')

// Printing result of method
console.log(a);

Output

-1

We have a complete list of Javascript Array methods, to check those please go through this Javascript Array Complete reference article.

Supported Browsers: The browsers supported by JavaScript Array indexOf() method are listed below: 

• Google Chrome 1 and above
• Edge 12 and above
• Firefox 1.5 and above
• Internet Explorer 9 and above
• Opera 9.5 and above
• Safari 3 and above

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