title: Validate email with jQuery
body: <p>I have <code>input name="email"</code> and a <code>button</code> on the page.</p>
  
  <p>How do I validate this input in live for a valid email address? And add some class for a button, class "active" if it is valid or "inactive".</p>
  
  <p>This is a small task, so I don't want to use a plugins.</p>
  
  <p>Thanks</p>