Find missing letter in list of alphabets

Question

I am trying to solve the following issue:

Find the missing letter in the passed letter range and return it. If all letters are present in the range, return undefine

Answer 1

Note that you have a typo in alphabet: There are two "e"s.

You could split the string into an array, then use the some method to short-circuit the loop when you don't find a match:

function fearNotLetter(str) {
  var alphabet = 'abcdefghijklmnopqrstuvwxyz',
      missing,
      i= 0;
  
  str.split('').some(function(l1) {
    var l2= alphabet.substr(i++, 1);
    if(l1 !== l2) {
      if(i===1) missing= undefined;
      else      missing= l2;
      return true;
    }
  });
  
  return missing;
}

console.log(fearNotLetter('abce'));             //d
console.log(fearNotLetter('bcd'));              //undefined
console.log(fearNotLetter('abcdefghjklmno'));   //i
console.log(fearNotLetter('yz'));               //undefined