title: jQuery live search when 4 numbers entered
body: <p>How do I do a live search only once the user has typed in 4 numbers into the input?</p>
  
  <p>It basically needs to contact the php page using $ajax which I already have.</p>
  
  <p>I thought it might be an <code>input.length == 4</code> but I tried it and failed.</p>