http://www.codewars.com/kata/alternating-case-%3C-equals-%3E-alternating-case
Define String.prototype.toAlternatingCase (or a similar function/method such as to_alternating_case/toAlternatingCase/ToAlternatingCase in your selected language; see the initial solution for details) such that each lowercase letter becomes uppercase and each uppercase letter becomes lowercase.
For example:
"hello world".toAlternatingCase() === "HELLO WORLD"