Searching Arrays with indexOf and lastIndexOf

Description

The lastIndexOf() method compares searchElement to elements of the array using strict equality (the same algorithm used by the === operator). NaN values are never compared as equal, so lastIndexOf() always returns -1 when searchElement is NaN.

The lastIndexOf() method skips empty slots in sparse arrays.

The lastIndexOf() method is generic. It only expects the this value to have a length property and integer-keyed properties.