----------
20181216

Check is date ?
if (Object.prototype.toString.call(d) === "[object Date]") {
  // it is a date
  if (isNaN(d.getTime())) {  // d.valueOf() could also work
    // date is not valid
  } else {
    // date is valid
  }
} else {
  // not a date
}

Update [2018-05-31]: If you are not concerned with Date objects from other JS contexts (external windows, frames, or iframes), this simpler form may be preferred:
function isValidDate(d) {
  return d instanceof Date && !isNaN(d);
}


ref: 
https://stackoverflow.com/questions/1353684/detecting-an-invalid-date-date-instance-in-javascript


----------
All dates are calculated in milliseconds 
from 01 January, 1970 00:00:00 Universal Time (UTC) 
with a day containing 86,400,000 milliseconds.

var today = new Date()
var d1 = new Date("October 13, 1975 11:13:00")
var d2 = new Date(79,5,24)
var d3 = new Date(79,5,24,11,33,0)

var myDate=new Date();
myDate.setFullYear(2010,0,14);

var myDate=new Date();
myDate.setDate(myDate.getDate()+5); // 5 days in the future.


var d = new Date();
var d = new Date(milliseconds);
var d = new Date(dateString);
var d = new Date(year, month-1, day, hours, minutes, seconds, milliseconds); 
var gdRelease = new Date('1967/01/05')
var gdRelease = new Date(2010,1,10,13,1,1,2);
sDObj = new Date(y,m,1,0,0,0,0);


function printDate()
{
	myDate = new Date();
	alert("今天是"+myDate+"。");
}


function printDate()
{
	youbi = new Array("日","一", "二","三","四","五","六");
	myDate = new Date();
	theDate = myDate.getDate();
	theDay = youbi[myDate.getDay()];
	theFyear = myDate.getFullYear();
	theYear = myDate.getYear();
	theMonth = myDate.getMonth() + 1;
	document.write("西元"+theFyear+"("+theYear+")年"+theMonth+"月"+theDate+"日"+"星期"+theDay);
}


function printDate()
{
	youbi = new Array("日","一","二","三","四","五","六");
	myDate = new Date();
	myDate.setFullYear(2004);
	myDate.setMonth(8);
	myDate.setDate(29);
	theDate = myDate.getDate();
	theDay = youbi[myDate.getDay()];
	theFyear = myDate.getFullYear();
	theYear = myDate.getYear();
	theMonth = myDate.getMonth() + 1;
	document.write("西元"+theFyear+"("+theYear+")年"+theMonth+"月"+theDate+"日"+"星期"+theDay);
}

// Datetime begin
function ZGetSDateTime(vDate) {
	var s1 = (10000 + (vDate.getMonth()+1) * 100 + vDate.getDate()).toString();
	var s2 = (1000000 + vDate.getHours() * 10000 + vDate.getMinutes() * 100 + vDate.getSeconds()).toString();
	return vDate.getFullYear() + "." + s1.substr(1,2) + "." + s1.substr(3,2) + " " + s2.substr(1,2) + ":" + s2.substr(3,2) + ":" + s2.substr(5,2); 
}
// Datetime end