Edit in JSFiddle

//today
today = new Date();

//Thu Dec 25 2014 12:00:15 GMT+0900 (JST)
var Xmas14 = new Date("December 25, 2014 12:00:15");

//Sun Jan 25 2015 00:00:00 GMT+0900 (JST)
var Xmas14 = new Date(2014, 12, 25);

//Sun Jan 25 2015 10:30:00 GMT+0900 (JST) 
var Xmas14 = new Date(2014, 12, 25, 10, 30, 0);

//ISODate
var IPOdate = new Date();
IPOdate.setTime(Date.parse("Aug 9, 1995"));

//デジタル時計
function JSClock() {
  var time = new Date();
  var hour = time.getHours();
  var minute = time.getMinutes();
  var second = time.getSeconds();
  var temp = "" + ((hour > 12) ? hour - 12 : hour);
  if (hour == 0)
    temp = "12";
  temp += ((minute < 10) ? ":0" : ":") + minute;
  temp += ((second < 10) ? ":0" : ":") + second;
  temp += (hour >= 12) ? " P.M." : " A.M.";
  return temp;
}
JSClock();