JavaScript String indexOf() Method

The JavaScript String indexOf() method finds the index of the first occurrence of the argument string in the given string. The value returned is 0-based.

Syntax:

str.indexOf(searchValue , index)

Parameters: 

• searchValue: The searchValue is the string that is to be searched in the base string. 
• index: The index defines the starting index from where the search value is to be searched in the base string.

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

Example 1: Below is an example of the String indexOf() Method. 

JavaScript

function func() {

    // Original string
    let str = 'Departed Train';

    // Finding index of occurrence of 'Train'
    let index = str.indexOf('Train');
    console.log(index);
}
func();

Output:

9

Example 2: In this example, the indexOf() method finds the index of the string ed Tr. Since the first and only index where this string is present is 6, therefore this function returns 6 as the answer.

JavaScript

// JavaScript to illustrate indexOf() method
function func() {

    // Original string
    let str = 'Departed Train';

    // Finding index of occurrence of 'Train'
    let index = str.indexOf('ed Tr');
    console.log(index);
}
func();

Output: 

6

Example 3: In this example, the indexOf() method finds the index of the string Train. Since the searchValue is not present in the string, therefore this function returns -1 as the answer.

JavaScript

function func() {

    // Original string
    let str = 'Departed Train';

    // Finding index of occurrence of 'Train'
    let index = str.indexOf('train');
    console.log(index);
}
func();

Output: 

-1

Example 4: In this example, the indexOf() method finds the index of the string Train. Since the first index of the searchValue is 9, therefore this function returns 9 as the answer.

JavaScript

function func() {

    // Original string
    let str = 'Departed Train before another Train';

    // Finding index of occurrence of 'Train'
    let index = str.indexOf('Train');
    console.log(index);
}
func();

Output: 

9 

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

Supported browser:

• Chrome 1 and above
• Edge 12 and above
• Firefox 1 and above
• Internet Explorer 3 and above
• Opera 3 and above
• Safari 1 and above