JavaScript Date对象获取ISO周数和年份

JavaScript Date对象扩展，支持获取ISO周数和其年份。

 

/* 
date: 指定时间
mondayIsFirstDay: true周一是周的第一天
返回指定时间和其周最后一天的差值天数
*/
Date.prototype.getDayAddForWeekEnd = function(date, mondayIsFirstDay) {
    var  day = date.getDay();//默认周日是第一天
    var dayAdd = 6-day;
    if(mondayIsFirstDay){
        // 周一是第一天
        dayAdd = (7-day)%7;
    }
    return dayAdd;
}

/* 得到ISO周：一年中的第多少个星期
	mondayIsFirstDay: true周一是周的第一天
	返回数组：[年份,周数]
*/
Date.prototype.getYearAndWeek = function(mondayIsFirstDay) {
    var date = new Date(this.getTime());
    date.setHours(0, 0, 0, 0);
    var dayAdd = this.getDayAddForWeekEnd(date, mondayIsFirstDay);
    // 当前时间的周的最后一天
    date.setDate(date.getDate()+dayAdd);
    // January 4 is always in week 1.
    var week1 = new Date(date.getFullYear(), 0, 4);
    // 今年第一周的最后一天
    var wdayAdd = this.getDayAddForWeekEnd(week1, mondayIsFirstDay)
    week1.setDate(week1.getDate()+wdayAdd);
    if(date.getTime()<week1.getTime()){
        week1 = new Date(date.getFullYear()-1, 0, 4);
        // 去年第一周的最后一天
        var wdayAdd = this.getDayAddForWeekEnd(week1, mondayIsFirstDay)
        week1.setDate(week1.getDate()+wdayAdd);
    }
    // 相差多个个7天：1000*60*60*24*7=604800000
    var wnum = (date.getTime() - week1.getTime())/604800000
    return [week1.getFullYear(),Math.floor(1 + wnum)];
}

/* 得到ISO周：一年中的第多少个星期
	mondayIsFirstDay: true周一是周的第一天
*/
Date.prototype.getWeek = function(mondayIsFirstDay) {
    var yearAndWeek = this.getYearAndWeek(mondayIsFirstDay);
    return yearAndWeek[1];
}
/* 得到ISO周数的年份
mondayIsFirstDay: true周一是周的第一天
*/
Date.prototype.getWeekYear = function(mondayIsFirstDay) {
    var yearAndWeek = this.getYearAndWeek(mondayIsFirstDay);
    return yearAndWeek[0];
}