javascript获取指定时间函数

function WeekDate() {  
 
    /** 
     * 基准时间，所有计算以此为基础 
     */ 
    var _calcDate = new Date();  
 
    /** 
     * 一天的豪秒数 
     */ 
    var _day = 1000 * 60 * 60 * 24;  
 
    this.getThisWeekDate = getThisWeekDate;  
    this.getPrevWeekDate = getPrevWeekDate;  
    this.getNextWeekDate = getNextWeekDate;  
    this.wrapDate = wrapDate;  
 
    this.getDayMillisecond = getDayMillisecond;  
 
    /** 
     * 取上周开始至上周结束日期 
     * 
     * @return Array [0]上周第一天 [1]上周最后一天 
     */ 
    function getPrevWeekDate() {  
        // 取上周结束日期  
        var lastDay = new Date(_calcDate - (_calcDate.getDay()) * _day);  
        // 取上周开始日期  
        var firstDay = new Date((lastDay * 1) - 6 * _day);  
        // 更新基准时间  
        _calcDate = firstDay;  
 
        return [wrapDate(firstDay), wrapDate(lastDay)];  
    }  
 
    /** 
     * 取下周开始至下周结束日期 
     * 
     * @return Array [0]上周第一天 [1]上周最后一天 
     */ 
    function getNextWeekDate() {  
        // 取下周开始日期  
        var firstDay = new Date((_calcDate * 1) + (6 - _calcDate.getDay() + 2) * _day);  
        // 取下周结束日期  
        var lastDay = new Date((firstDay * 1) + 6 * _day);  
        // 更新基准时间          
        _calcDate = firstDay;  
 
        return [wrapDate(firstDay), wrapDate(lastDay)];  
    }  
   
    function getNextWeekFirstDay(){
    var next_week=getNextWeekDate()[0]+"";
    var next_week_day=next_week.split("-");
    //alert(next_week_day);
    return Number(next_week_day[2]);
    }
    /** 
     * 取本周开始至本周结束日期 
     * 
     * @return Array [0]本周第一天 [1]本周最后一天 
     */ 
    function getThisWeekDate() {  
        _calcDate = new Date();  
        // 第一天日期  
        var firstDay = new Date(_calcDate - (_calcDate.getDay() - 1) * _day);  
        // 最后一天日期  
        var lastDay = new Date((firstDay * 1) + 6 * _day);  
 
        return [wrapDate(firstDay), wrapDate(lastDay)];  
    }  
 
    function wrapDate($date) {  
        var m = $date.getMonth() + 1;  
        m = m < 10 ? "0" + m : m;  
 
        var d = $date.getDate();  
        d = d < 10 ? "0" + d : d;  
 
        return $date.getFullYear() + "-" + m + "-" + d;              
    }  
 
    function getDayMillisecond() {  
        return _day;  
    }  
}