js 日期格式化及日期增减

//Demo:new Date().format("yyyy-MM-dd hh:mm:ss.SSS")
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;
}

Date.prototype.addYears = function (num) {
    num = parseInt(num);

    var sYear = this.getFullYear();
    var sMonth = this.getMonth();
    var sDay = this.getDate();


    var eYear = sYear + num;
    var eMonth = sMonth;
    var eDay = sDay;

    var eDate = new Date(eYear, eMonth, eDay);

    while (eDate.getMonth() != eMonth) {
        eDay--;
        eDate = new Date(eYear, eMonth, eDay);
    }

    var times = eDate.getTime() - new Date(sYear, sMonth, sDay).getTime();
    return new Date(new Date().getTime() + times);
}
//Demo:new Date().addMonths(-1)
Date.prototype.addMonths = function (num) {
    num = parseInt(num);

    var sYear = this.getFullYear();
    var sMonth = this.getMonth() + 1;
    var sDay = this.getDate();

    var eYear = sYear;
    var eMonth = sMonth + num;
    var eDay = sDay;
    while (eMonth > 12) {
        eYear++;
        eMonth -= 12;
    }
    while (eMonth <= 0) {
        eYear--;
        eMonth += 12;
    }

    var eDate = new Date(eYear, eMonth - 1, eDay);

    while (eDate.getMonth() != eMonth - 1) {
        eDay--;
        eDate = new Date(eYear, eMonth - 1, eDay);
    }

    var times = eDate.getTime() - new Date(sYear, sMonth - 1, sDay).getTime();
    return new Date(new Date().getTime() + times);
}

Date.prototype.addDates = function (num) {
    return this.addHours(num * 24);
}
Date.prototype.addHours = function (num) {
    return this.addMinutes(num * 60);
}
Date.prototype.addMinutes = function (num) {
    return this.addSeconds(num * 60);
}

Date.prototype.addSeconds = function (num) {
    num = parseInt(num);
    return new Date(new Date().getTime() + num * 1000);
}