js 计算是今天多少周

/**
* 判断年份是否为润年
*
* @param {Number} year
*/
function isLeapYear(year) {
return (year % 400 == 0) || (year % 4 == 0 && year % 100 != 0);
}
/**
* 获取某一年份的某一月份的天数
*
* @param {Number} year
* @param {Number} month
*/
function getMonthDays(year, month) {
return [31, null, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31][month] || (isLeapYear(year) ? 29 : 28);
}
/**
* 获取某年的某天是第几周
* @param {Number} y
* @param {Number} m
* @param {Number} d
* @returns {Number}
*/
function getWeekNumber(y, m, d) {
var now = new Date(y, m - 1, d),
year = now.getFullYear(),
month = now.getMonth(),
days = now.getDate();
//那一天是那一年中的第多少天
for (var i = 0; i < month; i++) {
days += getMonthDays(year, i);
}

//那一年第一天是星期几
var yearFirstDay = new Date(year, 0, 1).getDay() || 7;

var week = null;
if (yearFirstDay == 1) {
week = Math.ceil(days / yearFirstDay);
} else {
days -= (7 - yearFirstDay + 1);
week = Math.ceil(days / 7) + 1;
}

return week;
}
var lot;
function loaddate(){
var now = new Date();
var str = now.getFullYear()+"-"+((now.getMonth()+1)<10?"0":"")+(now.getMonth()+1)+"-"+(now.getDate()<10?"0":"")+now.getDate();
var year = now.getFullYear();
var month =((now.getMonth()+1)<10?"0":"")+(now.getMonth()+1);
var date=(now.getDate()<10?"0":"")+now.getDate();
document.getElementById("RFLOT_DATE").value=str;
var ttwo=year.toString().substring(2,year.length);
lot=ttwo+month+date;
//document.getElementById("RFLOT_LOT").value=getWeekNumber(year,month,date)+ttwo;

}