Edit in JSFiddle

/**
 * Daylight Savings Time
 *
 * Since 2007 DST begins on the second sunday of March,
 * and ends on the first sunday of November.
 *
 * @see http://www.nist.gov/pml/div688/dst.cfm
 * @author Dan Alloway <dan@micahsix.com>
 */

var currentDate = new Date();
var currentYear = currentDate.getFullYear();

// DST Start
var firstOfMarch = new Date(currentYear, 2, 1);
var daysUntilFirstSundayInMarch = (7 - firstOfMarch.getDay()) % 7;
var secondSundayInMarch = firstOfMarch.getDate() + daysUntilFirstSundayInMarch + 7;
var dstStartDate = new Date(currentYear, 2, secondSundayInMarch);

// DST End
var firstOfNovember = new Date(currentYear, 10, 1);
var daysUntilFirstSundayInNov = (7 - firstOfNovember.getDay()) % 7;
var firstSundayInNovember = firstOfNovember.getDate() + daysUntilFirstSundayInNov;
var dstEndDate = new Date(currentYear, 10, firstSundayInNovember);

document.getElementById("dstStart").innerHTML = "DST begins on: " + dstStartDate;
document.getElementById("dstEnd").innerHTML = "DST ends on: " + dstEndDate;
<div id="dstStart"></div>
<div id="dstEnd"></div>