syntax:

string.lastIndexOf(substring[, offset])

where:

substring - The substring that is to be searched for within string

offset - An optional integer argument which specifies the position within string at which the search is to start. Default is 0.

return:

number - index of the last appearance of a substring in a string, else -1, if substring not found.

see:

String indexOf()

description:

This method is similar to String indexOf(), except that it finds the last occurrence of a character in a string instead of the first.