JS获取年月日

function DateSelector(selYear, selMonth, selDay) {
    this.selYear = selYear;
    this.selMonth = selMonth;
    this.selDay = selDay;
    this.selYear.Group = this;
    this.selMonth.Group = this;
    if (window.document.all != null) {
        this.selYear.attachEvent("onchange", DateSelector.Onchange);
        this.selMonth.attachEvent("onchange", DateSelector.Onchange);
    }
    else {
        this.selYear.addEventListener("change", DateSelector.Onchange, false);
        this.selMonth.addEventListener("change", DateSelector.Onchange, false);
    }
    if (arguments.length == 4) {
        this.InitSelector(arguments[3].getFullYear(), arguments[3].getMonth() + 1, arguments[3].getDate());
    }
    else if (arguments.length == 6) {
        this.InitSelector(arguments[3], arguments[4], arguments[5]);
    }
    else {
        var dt = new Date();
        this.InitSelector(dt.getFullYear(), dt.getMonth() + 1, dt.getDate());
    }
}
DateSelector.prototype.MinYear = 1900;
DateSelector.prototype.MaxYear = (new Date()).getFullYear();
DateSelector.prototype.InitYearSelect = function () {
    for (var i = this.MaxYear; i >= this.MinYear; i--) {
        var op = window.document.createElement("option");
        op.value = i;
        op.innerHTML = i;
        this.selYear.appendChild(op);
    }
}
DateSelector.prototype.InitMonthSelect = function () {
    for (var i = 1; i < 13; i++) {
        var op = window.document.createElement("OPTION");
        op.value = i;
        op.innerHTML = i;
        this.selMonth.appendChild(op);
    }
}
DateSelector.DaysInMonth = function (year, month) {
    var date = new Date(year, month, 0);
    return date.getDate();
}
DateSelector.prototype.InitDaySelect = function () {
    var year = parseInt(this.selYear.value);
    var month = parseInt(this.selMonth.value);
    var daysInMonth = DateSelector.DaysInMonth(year, month);
    this.selDay.options.length = 0;
    for (var i = 1; i <= daysInMonth; i++) {
        var op = window.document.createElement("option");
        op.value = i;
        op.innerHTML = i;
        this.selDay.appendChild(op);
    }
}
DateSelector.Onchange = function (e) {
    var selector = window.document.all != null ? e.srcElement : e.target;
    selector.Group.InitDaySelect();
}
DateSelector.prototype.InitSelector = function (year, month, day) {
    this.selYear.options.length = 0;
    this.selMonth.options.length = 0;
    this.InitYearSelect();
    this.InitMonthSelect();
    this.selYear.selectedIndex = this.MaxYear - year;
    this.selMonth.selectedIndex = month - 1;
    this.InitDaySelect();
    this.selDay.selectedIndex = day - 1;
}

//调用
window.onload = function () {
    var selYear = window.document.getElementById("selYear");
    var selMonth = window.document.getElementById("selMonth");
    var selDay = window.document.getElementById("selDay");
    new DateSelector(selYear, selMonth, selDay, 2004, 2, 29);
}