Description

The JavaScript method lastIndexOf() returns the index of the last occurrence of a specific substring in a string.

Syntax

The method lastIndexOf() has the below syntax

It checks for the substring searchString in the string str from index fromIndex to end of the string str.

str.lastIndexOf(searchString, fromIndex)

Parameters

The method lastIndexOf() accepts the below parameters.

searchString

  • It is the string to be searched for within the string str.

fromIndex (optional)

  • It is the index within str to begin searching for searchString in backward.
  • The default value is Infinity.

Result

The method lastIndexOf() returns the below values.

  • Returns the index of the last occurrence of searchString if found in str, otherwise returns -1.

Example 1: Using the Method

The method returns the index of the last occurrence of a substring in a string.

var str = "Hello World!";

// Finding the index of the last occurrence of "o"
document.write(str.lastIndexOf("o"));         // Prints: 7

// Finding the index of the last occurrence of empty string
document.write(str.lastIndexOf(""));          // Prints: 12

// Finding the index of the last occurrence of "abc"
document.write(str.lastIndexOf("abc"));       // Prints: -1

Output:

7
13
-1

Example 2: Using the Method with From Index

The fromIndex is used to find the position from where the backward search must perform within the string.

var str = "Hello World!";

// Searches for "o" from index 2
document.write(str.lastIndexOf("o", 10));     // Prints: 7

// Searches for "o" from index 5
document.write(str.lastIndexOf("o", 5));     // Prints: 4

// Searches for "o" from index 10
document.write(str.lastIndexOf("o", 2));    // Prints: -1

Output:

7
4
-1

Overall

The JavaScript method lastIndexOf() returns the index of the last occurrence of a specific substring in a string.

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