js扩展Date对象 日期格式化

Date.prototype.format = function (format) {
    if (!format) {
        format = 'yyyy-MM-dd';//默认1997-01-01这样的格式
    }
    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;
}
//增加月份
Date.prototype.addMonths = function (m) {
    var d = this.getDate();
    this.setMonth(this.getMonth() + m);
    if (this.getDate() < d)
        this.setDate(0);
};
//增加日期
Date.prototype.addDays = function (d) {
    this.setDate(this.getDate() + d);
};