my diff_letters function
function diff_letters(word) {
  var arr = word.split('');
  Sort(arr);
  for (var i=0; i<(arr.length-1); i++) {
    if (arr[i]==arr[i+1]) return false;
  }
  return true;
}

You probably had i<3. I decided to make my function more general and introduce you to the length property of an array at the same time. Maybe you'll want to create a Words 5 game when we finish?

array of words with all letters different

More on arrays: we can add an item to an array using the push function. For example: if we had an array called words and we wanted to add the item word to the array:

  words.push(word);

In your words4.html fill the array words with words that have each letter different.

<script src='words4.js'></script>
<script src='Sort.js'></script>
<script src='diff_letters.js'></script>
<script>
  var words = [];
  for (var i=0; i<words4.length; i++) {
    if (diff_letters(words4[i])) {
      words.push(words4[i]);
    }
  }
</script>