title: jquery - date calculation
body: <p>My question is simple.</p>
  
  <pre><code>jQuery('#from').val(jQuery('#to').val());
  </code></pre>
  
  <p>I want to set the <code>jQuery('#from')</code> value to <code>jQuery('#to')</code> - 28 days.</p>
  
  <p>For now, the format of date is <code>mm/dd/yyyy</code>   ex) 04/21/2014</p>
  
  <p><code>jQuery('#to').val()</code> is 04/21/2014</p>
  
  <p>what function should I use to calculate the date?</p>