javascript 格式化日期显示

Date.prototype.format = function (format) //author: meizz 
{
    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;
}
alert(new Date().format("yyyy-MM-dd"));
alert(new Date("january 12 2008 11:12:30").format("yyyy-MM-dd hh:mm:ss"));