JavaScript Array indexOf() Method

Last Updated : 01 Nov, 2021

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

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Example:

<script>
    var name = [ 'gfg', 'cse', 'geeks', 'portal' ];

    a = name.indexOf('gfg')

    // Printing result of method
    document.write(a);
</script>
Output:
```
0
```

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)

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

element: This parameter holds the element which index will be return.
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 examples illustrate the Array indexOf() method in JavaScript:

Example 1: In this example the method will searched for the element 2 in that array return that element indesx.
```
Input : [1, 2, 3, 4, 5].indexOf(2);
Output: 1
```
Example 2: In this example the method will searched for the 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:

<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:

Program 2:

<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
    document.write(a);
</script>