jquery模拟生日日期下拉选择框

现在有很多关于日期的插件，但是都是年、月、日以日历的形式出现，我在项目有需求是日期以下拉框的形式完成。如图：

//HTML代码如下；

　　　　　　<div class="phone_mation">
              <div class="weui-cell__hd" id="birth">
                <label class="weui-label"><span>* </span>生日</label>
                <div class="birth-r">
                  <div class="year">
                    <select id="date-sel-year" rel="1985" class="cx_nd"></select>
                  </div>
                  <div class="year">
                    <select id="date-sel-month" rel="10" class="cx_nd"></select>
                  </div>
                  <div class="year">
                    <select id="date-sel-day" rel="01" class="cx_nd"></select>
                  </div>
                </div>
              </div>
            </div>



//需要引入插件：
   // 出生年月插件
    $.date_picker({
          YearSelector:  "#date-sel-year",
          MonthSelector: "#date-sel-month",
          DaySelector:   "#date-sel-day"
    });

插件代码：在html文件引入这个js文件和jquery文件即可；

(function($){
    $.extend({
        date_picker: function(options){
            var defaults = {
                YearSelector: "#sel_year",
                MonthSelector: "#sel_month",
                DaySelector: "#sel_day",
                FirstText: "",
                FirstValue: 0
            };
            var opts = $.extend({}, defaults, options);
            var $YearSelector = $(opts.YearSelector);
            var $MonthSelector = $(opts.MonthSelector);
            var $DaySelector = $(opts.DaySelector);
            var FirstText = opts.FirstText;
            var FirstValue = opts.FirstValue;
    
            // 初始化
            var str = "<option value="" + FirstValue + "">" + FirstText + "</option>";
            $YearSelector.html(str);
            $MonthSelector.html(str);
            $DaySelector.html(str);
    
            // 年份列表
            var yearNow = new Date().getFullYear();
            var yearSel = $YearSelector.attr("rel");
            for (var i = yearNow; i >= 1900; i--) {
                var sed = yearSel==i?"selected":"";
                var yearStr = "<option value="" + i + "" " + sed+">" + i + "</option>";
                $YearSelector.append(yearStr);
            }
    
            // 月份列表
            var monthSel = $MonthSelector.attr("rel");
            for (var i = 1; i <= 12; i++) {
                var monthStr=null;
                var sed = monthSel==i?"selected":"";
                if(i<10){
                    monthStr="<option value="" + i + "" "+sed+">" + '0' +i + "</option>";
                }else{
                    monthStr = "<option value="" + i + "" "+sed+">"  +i + "</option>";
                }
                $MonthSelector.append(monthStr);
            }
    
            // 日列表(仅当选择了年月)
            function BuildDay() {
                if ($YearSelector.val() == 0 || $MonthSelector.val() == 0) {
                    // 未选择年份或者月份
                    $DaySelector.html(str);
                } else {
                    $DaySelector.html(str);
                    var year = parseInt($YearSelector.val());
                    var month = parseInt($MonthSelector.val());
                    var dayCount = 0;
                    switch (month) {
                        case 1:
                        case 3:
                        case 5:
                        case 7:
                        case 8:
                        case 10:
                        case 12:
                            dayCount = 31;
                            break;
                        case 4:
                        case 6:
                        case 9:
                        case 11:
                            dayCount = 30;
                            break;
                        case 2:
                            dayCount = 28;
                            if ((year % 4 == 0) && (year % 100 != 0) || (year % 400 == 0)) {
                                dayCount = 29;
                            }
                            break;
                        default:
                            break;
                    }
                    
                    var daySel = $DaySelector.attr("rel");
                    for (var i = 1; i <= dayCount; i++) {
                        var dayStr=null;
                        var sed = daySel==i?"selected":"";
                        if(i<10){
                            // dayStr = "<option value="" + i + "" "+sed+">" + +'0'+i + "</option>";
                            dayStr =`<option value=i ${sed}>0${i}</option>`

                        }else{
                            // dayStr = "<option value="" + i + "" "+sed+">" + i + "</option>";
                            dayStr =`<option value=i ${sed}>${i}</option>`
                        }
                        $DaySelector.append(dayStr);
                    }
                }
            }
            $MonthSelector.change(function () {
                BuildDay();
            });
            $YearSelector.change(function () {
                BuildDay();
            });
            if($DaySelector.attr("rel")!=""){
                BuildDay();
            }
        }
    });
})(jQuery);