<form name="form1" id="dateForm">  <select name="year"></select>年  <select name="month"></select>月  <select name="day"></select>日</form>

$(function(){  var i=1945;  var date=new Date();  var year=date.getFullYear();//獲取當前年份  var dropList;  for(var i;i<2017;i++){    if(i==year){      dropList=dropList+"<option value='"+i+"' selected>"+i+"</option>";    }else {      dropList=dropList+"<option value='"+i+"'>"+i+"</option>";    }  }  $('#dateForm select[name=year]').html(dropList);//生成年份下拉列表  var monthly;  for(var j=1;j<13;j++){    monthly=monthly+'<option value="'+j+'">'+j+'</option>'  }  $('#dateForm select[name=month]').html(monthly);//生成月份下拉列表  var daily;  for(var day=1;day<=31;day++){    daily=daily+'<option value="'+day+'">'+day+'</option>';  }  $('#dateForm select[name=day]').html(daily);  $('#dateForm select[name=month]').change(function(){    var currentDay;    var total;    var flag=$('#dateForm select[name=year]:selected').val();    var currentMonth=$('#dateForm select[name=month]').val();    switch (currentMonth){      case "1":      case "3":      case "5":      case "7":      case "8":      case "10":      case "12":total=31;break;      case "4":      case "6":      case "9":      case "11":total=30;break;      case "2":        //閏年 整除4但是不整除100 或者整除400        if( (flag%4==0 && flag%100!=0 ) || flag%400){          total=29;        }else {          total=28;        }      default :break    }    for(day=1;day<=total;day++){      currentDay=currentDay+'<option value="'+day+'">'+day+'</option>'    }    $('#dateForm select[name=day]').html(currentDay);//生成日期下拉列表  });});