JS如何将UTC格式时间转本地格式

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; 
} 

var TempDate = new Date(); 

TempDate.toLocaleDateString()//2013年9月4日 

TempDate.format("yyyy-MM-dd")//2013-09-04