[Белый шум]

var date = function (date) {
    var obj = {
        _value: null,
        get value() {
            return this+"";
        },
        init: function(date) {
            if(date instanceof Date) this._value = date;
            else {
            var arr = date.split(/[\s:-]/);
            this._value = new Date(Date.UTC(arr[0], arr[1] - 1, arr[2], arr[3], arr[4]));
            }
            return this;
        },
        add: function(value, type) {
                if (value > 0 && type in this.method) {
                    return this.setValue(value, this.method[type]);
                } else {
                    throw new TypeError("Передано неверное значение");
                }
        },
        subtract: function(value, type) {
            if (value > 0 && type in this.method) {
                return this.setValueSubtract(value, this.method[type]);
            } else {
                throw new TypeError("Передано неверное значение");
            }
        },
        method: {
            "years": "FullYear",
            "months": "Month",
            "days": "Date",
            "hours": "Hours",
            "minutes": "Minutes"
        },
        setValue: function(value, method) {
            this._value['setUTC' + method](value + this._value['getUTC' + method]());
            return this;
        },
        setValueSubtract: function(value, method) {
            this._value['setUTC' + method](-value + this._value['getUTC' + method]());
            return this;
        },
        valueOf: function() {
                var year = this._value.getFullYear();
                var month = this._value.toLocaleString("ru",{timeZone : "UTC",month: '2-digit'});
                var day = this._value.toLocaleString("ru",{timeZone : "UTC",day: '2-digit'});
                var time = this._value.toLocaleString("ru",{timeZone : "UTC", hour: '2-digit', minute: '2-digit' });
                var dates = year + "-" + month + "-" + day + " " + time;
                return dates;
        },
        toString: this.valueOf,
    };
    return obj.init(date);
};

var time = date('2017-05-16 13:45')
    .add(24, 'hours')
    .subtract(1, 'months')
    .add(3, 'days')
    .add(15, 'minutes');
var time2 = date("2017-04-20 14:00");

alert(time);
alert(time == "2017-04-20 14:00");
alert(time+"" == time2+"");
console.log('time.value:', time.value);
console.log('time2:', time2);

Материалы для изучения:
https://learn.javascript.ru/object-conversion
https://learn.javascript.ru/descriptors-getters-setters

P.S.: хз, ответил я на вопрос или нет, но больше ничем помочь не могу.