js日期重写

Date.prototype.Format = function (fmt) {
    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 today = new Date();
alert(today.Format("yyyy-MM-dd"));