JS String Prototype LastIndexOf

JavaScript String prototype lastIndexOf

The lastIndexOf() method returns the index within the calling String object of the last occurrence of the specified value, or -1 if not found. The calling string is searched backward, starting at fromIndex.

Syntax

str.lastIndexOf(searchValue[, fromIndex])

Parameters

searchValue

A string representing the value to search for.

fromIndex

Optional. The location within the calling string to start the search at, indexed from left to right. It can be any integer. The default value is str.length. If it is negative, it is treated as 0. If fromIndex > str.length, fromIndex is treated as str.length.

MDN link | MSDN link

Returns

Returns the last occurrence of a substring in the string.

Description

Characters in a string are indexed from left to right. The index of the first character is 0, and the index of the last character is stringName.length - 1.

The lastIndexOf() method is case sensitive. For example, the following expression returns -1:

Examples

'canal'.lastIndexOf('a');     // returns 3
'canal'.lastIndexOf('a', 2);  // returns 1
'canal'.lastIndexOf('a', 0);  // returns -1
'canal'.lastIndexOf('x');     // returns -1
'Blue Whale, Killer Whale'.lastIndexOf('blue'); // returns -1

var anyString = 'Brave new world';

console.log('The index of the first w from the beginning is ' + anyString.indexOf('w'));
// logs 8
console.log('The index of the first w from the end is ' + anyString.lastIndexOf('w')); 
// logs 10
console.log('The index of "new" from the beginning is ' + anyString.indexOf('new'));
// logs 6
console.log('The index of "new" from the end is ' + anyString.lastIndexOf('new'));
// logs 6

var str = "time, time";

var s = "";
s += "time is at position " + str.lastIndexOf("time");
s += "<br />";
s += "abc is at position " + str.lastIndexOf("abc");

document.write(s);

// Output:
// time is at position 6
// abc is at position -1