missingletters.js

// Bonfire: Missing letters
// Author: @codebubb
// Challenge: http://www.freecodecamp.com/challenges/bonfire-missing-letters?solution=function%20fearNotLetter(str)%20%7B%0A%20str%20%3D%20str.split(%27%27).map(function(c%2C%20i)%7B%0A%20%20%20%20%20%20return%20(c.charCodeAt()%20!%3D%20str.charCodeAt()%20%2B%20i)%20%3F%20String.fromCharCode(str.charCodeAt()%2Bi)%20%3A%20%27undefined%27%3B%0A%20%7D)%3B%0A%20return%20str.lastIndexOf(%27undefined%27)%20%3F%20str%5Bstr.lastIndexOf(%27undefined%27)%2B1%5D%20%3A%20%27undefined%27%3B%0A%20%09%0A%7D
// Learn to Code at Free Code Camp (www.freecodecamp.com)

function fearNotLetter(str) {
 str = str.split('').map(function(c, i){
      return (c.charCodeAt() != str.charCodeAt() + i) ? String.fromCharCode(str.charCodeAt()+i) : 'undefined';
 });
 return str.lastIndexOf('undefined') ? str[str.lastIndexOf('undefined')+1] : 'undefined';
 	
}