// Write a function which takes in a string
// and returns counts of each character in the string.

function charCount(str) {
    // 1. Make object to return at end.
    var obj = {};
    // 2. Loop over string, for each character
    for (var char of str) {
        // 2.a) If the character is a number/letter AND
        //      is a key in object, add 1 to count.
        // 2.b) If the character is a number/letter AND
        //      not in object, add it to the object and
        //      set value to 1.
        // 2.c) If character is something else (space, period, etc)
        //      don't do anything.
        if (isAlphaNumeric(char)) {
            char = char.toLowerCase();
            obj[char] = ++obj[char] || 1;
        }
    }
    // 3. Return object at end.
    return obj;
}

function isAlphaNumeric(str) {
  var code;

  for (var i = 0, len = str.length; i < len; i++) {
    code = str.charCodeAt(i);
    if (!(code > 47 && code < 58) && // numeric (0-9)
        !(code > 64 && code < 91) && // upper alpha (A-Z)
        !(code > 96 && code < 123)) { // lower alpha (a-z)
      return false;
    }
  }
  return true;
}