SO fiddle

Test Fiddle mainly for SO Questions

by Nick Craver

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/overcast/jquery-ui.css">
<p>Date: <input type="textbox" id="datepicker" /></p>

JavaScript

var d1s = new Date(2010, 8, 1),
    d1e = new Date(2010, 8, 20),
    d2s = new Date(2010, 9, 1),
    d2e = new Date(2010, 9, 20);

$(function() {
  $("#datepicker").datepicker({
    numberOfMonths: 1,
    beforeShowDay: function(date) {
      return [(date >= d1s && date <= d1e || date >= d2s && date <= d2e), ''];
    },
    minDate: d1s,
    maxDate: d2e
  });
});