JavaScript: The Definitive Guide, 6th Edition

Name

String.lastIndexOf() — search a string backward

Synopsis

string.lastIndexOf(substring)
string.lastIndexOf(substring, start)

Arguments

substring

The substring to be searched for within string.

start

An optional integer argument that specifies the position within string where the search is to start. Legal values are from 0 (the position of the first character in the string) to string .length−1 (the position of the last character in the string). If this argument is omitted, the search begins with the last character of the string.

Returns

The position of the last occurrence of substring within string that appears before the start position, if any, or −1 if no such occurrence is found within string.

Description

String.lastIndexOf() searches the string from end to beginning to see if it contains an occurrence of substring. The search begins at position start within string, or at the end of string if start is not specified. If an occurrence of substring is found, String.lastIndexOf() returns the position of the first character of that occurrence. Since this method searches from end to beginning of the string, the first occurrence found is the last one in the string that occurs before the start position.

If no occurrence of substring is found, String.lastIndexOf() returns −1.

Note that although String.lastIndexOf() searches string from end to beginning, it still numbers character positions within string from the beginning. The first character of the string has position 0, and the last has position ...