JavaScript String indexOf() Method

05 Oct, 2021
Below is the example of the String indexOf() Method.  
Example:
JavaScript
// 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
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
// 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:
JavaScript
<script>// JavaScript to illustrate indexOf() functionfunction 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
// 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
// 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 
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
nikhilchhipa9
ysachin2314
javascript-string
JavaScript
Web Technologies
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.
Difference between var, let and const keywords in JavaScript
Differences between Functional Components and Class Components in React
Remove elements from a JavaScript Array
Roadmap to Learn JavaScript For Beginners
Difference Between PUT and PATCH Request
Installation of Node.js on Linux
Top 10 Projects For Beginners To Practice HTML and CSS Skills
Difference between var, let and const keywords in JavaScript
How to insert spaces/tabs in text using HTML/CSS?
How to fetch data from an API in ReactJS ?