Array#lastIndexOf(item[, offset]) → Number

• item (?) – A value that may or may not be in the array.
• offset (Number) – The number of items at the end to skip before beginning the search.

Returns the position of the last occurrence of item within the array — or -1 if item doesn't exist in the array.

Array#lastIndexOf acts as an ECMAScript 5 polyfill. It is only defined if not already present in the user's browser, and it is meant to behave like the native version as much as possible. Consult the ES5 specification for more information.