title: Run setTimeout only when tab is active
body: <p>Is there a way to stop <code>setTimeout("myfunction()",10000);</code> from counting up when the page isn't active.  For instance,</p>
  
  <ol>
  <li>A user arrives at a "some page" and stays there for 2000ms</li>
  <li>User goes to another tab, leaves "some page" open.</li>
  <li><code>myfunction()</code> doesn't fire until they've come back for another 8000ms.</li>
  </ol>