JavaScript String lastIndexOf() Method

The lastIndexOf() method in JavaScript is used to search for the last occurrence of a specified substring within a string.

It returns the index of the last occurrence of the specified substring, or -1 if the substring is not found.

Syntax:

str.lastIndexOf(searchValue , index)

Parameters:

lastIndexOf() Method accepts 2 parameters which are discussed below:

• searchvalue: The searchvalue is the string that is to be searched in the base string.
• index: defines the starting index from where the searchvalue is to be searched in the base string backward

Return value:

This method returns the index of the string (0-based) where the searchvalue is found for the last time. If the searchvalue cannot be found in the string then the method returns -1

Example 1: Finding Last Occurrence of Substring in JavaScript

The function func() initializes a string variable str with the value 'GeeksforGeeks'. It then uses the lastIndexOf() method to find the index of the last occurrence of the substring 'for' within the string str. The index, which is 5, is then printed to the console.

function func() {
    let str = 'GeeksforGeeks';
    let index = str.lastIndexOf('for');
    console.log(index);
}
func();

5

Example 2: Case-sensitive Search with JavaScript's lastIndexOf()

The func() function initializes a string variable str with the value 'Departed Train'. It then uses the lastIndexOf() method to find the index of the last occurrence of the substring 'train' (case-sensitive) within the string str. Since 'train' is not found in 'Departed Train', -1 is printed to the console.

// JavaScript to illustrate lastIndexOf() method

function func() {

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

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

-1

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

Supported Browsers: 

• Google Chrome 3
• Microsoft Edge 12
• Mozilla Firefox 3.0
• Safari 5
• Opera 10.5