title: do an alert on keyup only if the key is a letter or number
body: <p>I would like to show an alert on keyup event but only if the key was a letter or a number, not for shift,tab etc.</p>
  
  <pre><code>&lt;input type='text' id='hi /&gt;
  </code></pre>
  
  <p>or for any key except for tab, shift, ctrl, enter</p>
  
  <p>anybody knows how ?</p>