js中将数字格式的日期化为yyyy-MM-dd样式

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;
}