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>