title: Count with A, B, C, D instead of 0, 1, 2, 3, ... with JavaScript
body: <p>This is probably an unusual request, but for my script I need a function that increments by letter instead of number. For example:</p>
  
  <p>This is a numeric example:</p>
  
  <pre><code>var i = 0;
  while(condition){
   window.write('We are at '+i);
   ++i;
  }
  </code></pre>
  
  <p>Essentially, I want to count with letters, like Microsoft Excel does, instead of numbers. So instead of printing "We are at 0", "We are at 1", "We are at 2", etc., I need to print "We are at A", "We are at B", "We are at C", etc.</p>
  
  <p>To mimic Excel (the only example I can think of), after reaching index 25 (Z), we could move on to 'AA', 'AB', 'AC', etc.</p>
  
  <p>So it would work great like so:</p>
  
  <pre><code>var i = 0;
  while(condition){
   window.write('We are at '+toLetter(i));
   ++i;
  }
  </code></pre>
  
  <p>Even better if somebody can write a function that then converts a letter back into a digit, i.e. toNumber('A') = 0 or toNumber('DC') = 107 (I think).</p>
  
  <p>Thanks!</p>