三级联动日历例题

<body>
       <select id="year"></select>年
       <select id="month"></select>月
       <select id="day"></select>日                       //设置年月日下拉框
   </body>

</html>
<script>
   var year = document.getElementById("year");                                                   定义年月日
   var month = document.getElementById("month");
   var day = document.getElementById("day");

   var time = new Date();                                                                                 定义时间获取时间
   year_now = time.getFullYear();

   for(var i = year_now - 100; i < year_now + 100; i++) {                                   添加年份
       year.innerHTML += "<option>" + i + "</option>"
   }
   for(var i = 1; i < 13; i++) {                                                                                添加月份
       month.innerHTML += "<option>" + i + "</option>";
   }

   function days(max) {                                                                                      根据月份定义天数
       day.innerHTML = "";
       for(var i = 1; i <= max; i++) {
           day.innerHTML += "<option value='"+i+"'>" + i + "</option>";
       }
   }

   year.onchange = function(){                                                                      给1、3、5、7、8、10、12月添加日期
       if( month.selectedOptions[0].innerHTML==1   ||
           month.selectedOptions[0].innerHTML==3   ||
           month.selectedOptions[0].innerHTML==5   ||
           month.selectedOptions[0].innerHTML==7   ||
           month.selectedOptions[0].innerHTML==8   ||
           month.selectedOptions[0].innerHTML==10 ||
           month.selectedOptions[0].innerHTML==12
       ){
           days(31);
       }else if(                                                                                                                如果不是31天月份则添加30天
           month.selectedOptions[0].innerHTML==4   ||
           month.selectedOptions[0].innerHTML==6   ||
           month.selectedOptions[0].innerHTML==9   ||
           month.selectedOptions[0].innerHTML==11
       ){
           days(30);
       }else{                                                                                                                                   给二月添加天数区分闰年平年
           var year_selected = year.selectedOptions[0].innerHTML;
           if((year_selected%4==0&&year_selected%100!=0)||year_selected%400==0){
               days(29);
           }else{
               days(28);
           }
       }
   }
   month.onchange = function(){                                                                                                         同上
       if( month.selectedOptions[0].innerHTML==1   ||
           month.selectedOptions[0].innerHTML==3   ||
           month.selectedOptions[0].innerHTML==5   ||
           month.selectedOptions[0].innerHTML==7   ||
           month.selectedOptions[0].innerHTML==8   ||
           month.selectedOptions[0].innerHTML==10 ||
           month.selectedOptions[0].innerHTML==12
       ){
           days(31);
       }else if(
           month.selectedOptions[0].innerHTML==4   ||
           month.selectedOptions[0].innerHTML==6   ||
           month.selectedOptions[0].innerHTML==9   ||
           month.selectedOptions[0].innerHTML==11
       ){
           days(30);
       }else{
           var year_selected = year.selectedOptions[0].innerHTML;
           if((year_selected%4==0&&year_selected%100!=0)||year_selected%400==0){
               days(29);
           }else{
               days(28);
           }
       }
   }
</script>