JavaScript Array indexOf() Method

The arr.indexOf() method is used to find the index of the first occurrence of the search element provided as the argument to the method. 

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.

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

Example 1:

javascript

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

Output:

0

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

Input : [1, 2, 3, 4, 5].indexOf(2);
Output: 1

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

Input : [1, 2, 3, 4, 5].indexOf(9);
Output: -1

Code for the above method is provided below

Program 1:

javascript

<script>
    // Taking input as an array A
    // having some elements.
    var 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.
    document.write(a);
</script>

Output:

1

Program 2:

javascript

<script>
    // Taking input as an array A
    // having some elements.
    var 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);
</script>

Output:

-1

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