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 just did this challenge. I am a beginner to Javascript so this was my approach, very simple, sometimes you don't have to use the methods they provide but they also help. I hope you can understand it.

function fearNotLetter(str) {

var alphabet= "abcdefghijlmnopqrstuvwxyz";
var piece =alphabet.slice(0, str.length+1);




for(var i=0; i < piece.length; i++ ){
if(str.charCodeAt(0) != 97){

return undefined;
}

else if(str.indexOf(piece[i])===-1){
  return piece[i];
}
}// for loop

}

fearNotLetter("abce");// It will return d
fearNotLetter("xy");//It will return undefined
fearNotLetter("bce");//It will return undefined