Missing Letters

missingLetters.js

function missingLetters(str) {
  var seq = "abcdefghijklmnopqrstuvwxyz";
  var firstEntry = seq.indexOf(str[0]);
  var missing = "";
  var missingCounter = 0;
  var j = 1;
  for (var i=firstEntry+1;i<firstEntry+str.length;i++){
    if (str.charCodeAt(j) != seq.charCodeAt(i+missingCounter)){
      missing = missing.concat(seq[i+missingCounter]);
      missingCounter = missingCounter+1;
    }
    j = j+1;
  }
  if (missing === ""){
    missing = undefined;
  }
  return missing;
}
missingLetters("bcd");

MissingLetters.markdown

Missing Letters

Finds the missing letter in the passed letter range and returns it. If all letters are present in the range, returns undefined.

A script by V.

License.