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

I think that you wanted to say that if a string doesn't start with "a" than return "undefined". So here's my code:

 function fearNotLetter(str) {
   var alphabet = ("abcdefgheijklmnopqrstuvwxyz");
   var i = 0;
   var j = 0;
   while (i < alphabet.length && j < str.length) {
     if (alphabet.charAt(i) != str.charAt(j)) {
       i++;
       j++;
       if (alphabet.charAt(i - 1) == "a") {
         return "undefined";
       } else {
         return (alphabet.charAt(i - 1));
       }
     }
     i++;
     j++;
   }
 }

 alert(fearNotLetter('abce'));

Here's the working JsFiddle.

You wanted the code to return the missing letter so I used CharAt.
You can make an array of letters and then search through it to see if it maches with letters from the string....