var year;
var month;
var day ;
var cYear=1983;
var cMonth=1;
var cDay=1;
var monthBases = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
  /***
   *初始化年月日
   */
function dateInit() {
	year = document.getElementById("birthyear");
    month = document.getElementById("birthmonth");
    day = document.getElementById("birthday");
	 //先给年下拉框赋内容
	var y = new Date().getFullYear();
	for (var i = 1900; i < y; i = i + 1) { //1900年到今
	    year.options.add(new Option(i, i));
	}
	
	 //赋月份的下拉框
	for (var i = 1; i < 13; i = i + 1) {
		month.options.add(new Option(i, i));
	}
	year.selectedIndex=cYear-1900
	month.selectedIndex=cMonth-1;
	var n = monthBases[cMonth-1];
	if (cMonth == 2 && IsPinYear(year.options[year.selectedIndex].value)) {
		n = n + 1;
	}//闰年2月加一天
	writeDay(n, day); //赋日期下拉框Author:meizz
	day.selectedIndex=cDay-1;
}
    /***
     *年发生变化时日期发生变化(主要是判断闰平年)
     */
function yearChange(yearv) {
	var Mvalue = month.options[month.selectedIndex].value;
	var n = monthBases[Mvalue - 1];
	if (Mvalue == 2 && IsPinYear(yearv)) {
		n = n + 1;//闰年2月加一天
	}
	writeDay(n, day);
}
   /***
    *月发生变化时日期联动
    */
function monthChange(monthv) {
	var Yvalue = year.options[year.selectedIndex].value;
	var n = monthBases[monthv - 1];
	if (monthv == 2 && IsPinYear(Yvalue)) {
		n = n + 1;//闰年2月加一天
	}
	writeDay(n, day);
}
   /***
    *据条件写日期的下拉框
    */
function writeDay(n, day) {
	var e = day;
	optionsClear(e);
	for (var i = 1; i < (n + 1); i = i + 1) {
		e.options.add(new Option(i, i));
	}
}
   /***
    *判断是否闰平年
    */
function IsPinYear(year) {
	return (0 == year % 4 && (year % 100 != 0 || year % 400 == 0));
}
   /***
    *清除下拉框
    */
function optionsClear(e) {
	 e.options.length=0;
}