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JavaScript String indexOf() Method
  • Last Updated : 31 Aug, 2020

Below is the example of the String indexOf() Method.

  • Example:




    // JavaScript to illustrate indexOf() function
    <script>
    function func() {
      
        // Original string
        var str = 'Departed Train';
      
        // Finding index of occurrence of 'Train'
        var index = str.indexOf('Train');
        document.write(index); 
    }
    func();
    </script>

    
    

  • Output:
    0
    

str.indexOf() function finds the index of the first occurrence of the argument string in the given string. The value returned is 0-based. The syntax of the function is as follows:

str.indexOf(searchValue , index)

Arguments:
the first argument to the function searchValue is the string that is to be searched in the base string. The second argument to the function index defines the starting index from where the searchValue is to be searched in the base string.

Return value:
This function returns the index of the string (0-based) where the searchValue is found for the first time. If the searchValue cannot be found in the string then the function returns -1.

Examples for the above function are provided below:



Example 1:

print('Departed Train'.indexOf('Train')); 

In this example the function indexOf() finds the index of the string Train. Since the first and the only index where this string is present is 9, therefore this function returns 9 as the answer.

Output:

9

Example 2:

print('Departed Train'.indexOf('ed Tr')); 

Output:

6

In this example the function indexOf() finds the index of the string ed Tr. Since the first and the only index where this string is present is 6, therefore this function returns 6 as the answer.

Example 3:

print('Departed Train'.indexOf('train')); 

Output:



-1

In this example the function indexOf() finds the index of the string Train. Since the searchValue is not present in the string, therefore this function returns -1 as the answer.

Example 4:

print('Departed Train before another Train'.indexOf('Train')); 

Output:

9

In this example the function indexOf() finds the index of the string Train. Since the first index of the searchValue is 9, therefore this function returns 9 as the answer.

Code for the above function are provided below:

Program 1:




// JavaScript to illustrate indexOf() function
<script>
function func() {
  
    // Original string
    var str = 'Departed Train';
  
    // Finding index of occurrence of 'Train'
    var index = str.indexOf('Train');
    document.write(index); 
}
func();
</script>


Output:

9

Program 2:




<script>
// JavaScript to illustrate indexOf() function
function func() {
  
    // Original string
    var str = 'Departed Train';
  
    // Finding index of occurrence of 'Train'
    var index = str.indexOf('ed Tr');
    document.write(index);  
}
func();
</script>  


Output:

6

Program 3:




// JavaScript to illustrate indexOf() function
<script>
function func() {
  
    // Original string
    var str = 'Departed Train';
  
    // Finding index of occurrence of 'Train'
    var index = str.indexOf('train');
    document.write(index);  
}
func();
</script>  


Output:

-1

Program 4:




// JavaScript to illustrate indexOf() function
<script>
function func() {
  
    // Original string
    var str = 'Departed Train before another Train';
  
    // Finding index of occurrence of 'Train'
    var index = str.indexOf('Train');
    document.write(index);  
}
func();
</script>  


Output:

9

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