javascript加减日期操作

<script type="text/javascript">
Date.prototype.Format = function(fmt) 
{
    //author: meizz 
    var o =
     { 
        "M+" : this.getMonth() + 1, //月份 
        "d+" : this.getDate(), //日 
        "h+" : this.getHours(), //小时 
        "m+" : this.getMinutes(), //分 
        "s+" : this.getSeconds(), //秒 
        "q+" : Math.floor((this.getMonth() + 3) / 3), //季度 
        "S" : this.getMilliseconds() //毫秒 
     }; 
    if (/(y+)/.test(fmt)) 
         fmt = fmt.replace(RegExp.$1, (this.getFullYear() + "").substr(4 - RegExp.$1.length)); 
    for (var k in o) 
        if (new RegExp("(" + k + ")").test(fmt)) 
             fmt = fmt.replace(RegExp.$1, (RegExp.$1.length == 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length))); 
    return fmt; 
}

Date.prototype.addDays = function(d)
{
    this.setDate(this.getDate() + d);
};

Date.prototype.addWeeks = function(w)
{
    this.addDays(w * 7);
};

Date.prototype.addMonths= function(m)
{
    var d = this.getDate();
    this.setMonth(this.getMonth() + m);
    if (this.getDate() < d)
        this.setDate(0);
};

Date.prototype.addYears = function(y)
{
    var m = this.getMonth();
    this.setFullYear(this.getFullYear() + y);
    if (m < this.getMonth()) 
     {
        this.setDate(0);
     }
};
var now = new Date();
now.addDays(10);//加减日期操作
alert(now.Format("yyyy-MM-dd"));
</script>

<script language="javascript">
//计算天数差的函数，通用 
   function DateDiff(sDate1, sDate2){    //sDate1和sDate2是 s1 = "2006-12-18" s2 = "2007-01-05" 
       var aDate, oDate1, oDate2, iDays 
       aDate = sDate1.split("-") 
       oDate1 = new Date(aDate[1] + '-' + aDate[2] + '-' + aDate[0])    //转换为12-18-2006格式 
       aDate = sDate2.split("-") 
       oDate2 = new Date(aDate[1] + '-' + aDate[2] + '-' + aDate[0]) 
       iDays = parseInt((oDate1 - oDate2) / 1000 / 60 / 60 /24)    //把相差的毫秒数转换为天数 
       return iDays 
   }    
   
var iDays =DateDiff( "2006-12-18","2007-01-05" );   
alert( iDays ) 
</script>