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();
Output
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();
Output
-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
JavaScript String lastIndexOf() Method – FAQs
What does lastIndexOf() do In JavaScript?
lastIndexOf() searches a string for a specified substring and returns the index of its last occurrence, or -1 if not found.
How do you use lastIndexOf() to find a substring?
Use str.lastIndexOf(searchValue) to find the last occurrence of searchValue in str, starting from the end of the string.
Is lastIndexOf() case-sensitive?
Yes, lastIndexOf() is case-sensitive. To perform a case-insensitive search, use methods like toLowerCase() on both str and searchValue.
Can lastIndexOf() search from a specific position?
Yes, str.lastIndexOf(searchValue, fromIndex) starts searching from fromIndex backwards. If omitted, it searches the entire string.
What does lastIndexOf() return if the substring is empty?
If searchValue is an empty string (“”), lastIndexOf() returns the position of the last character in str plus one.
We have a Cheat Sheet on Javascript where we covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.
