一个js的日期格式化函数

<script type="text/javascript">
Date.prototype.format = function(format)
{
var o = {
"M+" : this.getMonth()+1, //month

"d+" : this.getDate(), //day

"h+" : this.getHours(), //hour

"m+" : this.getMinutes(), //minute

"s+" : this.getSeconds(), //second

"q+" : Math.floor((this.getMonth()+3)/3), //quarter

"S" : this.getMilliseconds() //millisecond

}
if(/(y+)/.test(format))
format=format.replace(RegExp.$1,(this.getFullYear()+"").substr(4 - RegExp.$1.length));
for(var k in o)
if(new RegExp("("+ k +")").test(format))
format = format.replace(RegExp.$1,RegExp.$1.length==1 ? o[k] :("00"+ o[k]).substr((""+ o[k]).length));
return format;
}

var ddd = new Date();
document.write (ddd.format('yy-MM-dd'));
</script>