DaylightSavings.js

/**
 * isDST
 * Returns true if the supplied date (default Today) is DST
 */
var isDST = function(date) {
  date = date ? new Date(date) : new Date();    
  var winter = new Date(date.getFullYear(), 0, 1);
  return (date.getTimezoneOffset() !== winter.getTimezoneOffset());
};

/**
 * hasDST
 * Returns true if the supplied time zone (via date) observes DST
 */
var hasDST = function() {
  return isDST(new Date((new Date()).getFullYear(), 6, 1, 0, 0, 0, 0));
};

/**
 * Sample usage:
 *
 * console.log('hasDST', hasDST());
 * 
 * console.log('Today', isDST());
 * console.log('3/7/2009', isDST('3/7/2009'));
 * console.log('3/8/2009', isDST('3/8/2009'));
 * console.log('3/9/2009', isDST('3/9/2009'));
 * 
 * console.log('10/31/2009', isDST('10/31/2009'));
 * console.log('11/1/2009', isDST('11/1/2009'));
 * console.log('11/2/2009', isDST('11/2/2009'));
 * 
 */