[jQuery] retrieve value with JQuery

[Chuk]

Hi.  In one of my functions, I would like to test the value of a
certain field with an id="zipCode".  Here is my current code:

function retrieveCityState()
{
  if ($('#zipCode').value.length > 4)
  {
    ...
  }
}

This test doesn't seem to work.  How do I correctly handle this using
JQuery?  Thanks.