JavaScript-客製化日期選單

// 年度
var date = new Date();
var minYear = 1940,maxMonth = date.getFullYear(),
    selectYear = document.getElementById('selectYear');

for (var i = minYear; i<=maxMonth; i++){
    var opt = document.createElement('option');
    opt.value = i;
    opt.innerHTML = i;
    selectYear.appendChild(opt);
}

// 月份
var minMonth = 1,maxMonth = 12,
    selectMonth = document.getElementById('selectMonth');

for (var i = minMonth; i<=maxMonth; i++){
    var opt = document.createElement('option');
    opt.value = i;
    opt.innerHTML = i;
    selectMonth.appendChild(opt);
}

// 預設日期
daysInThisMonth();

// 日期
function daysInThisMonth() {
  var date_var = new Date(date.getFullYear(), date.getMonth()+1, 0).getDate();
  var minDay = 1,maxDay = date_var,
      selectDay = document.getElementById('selectDay');
    selectDay.options.length = 0;
  for (var i = minDay; i<=maxDay; i++){
      var opt = document.createElement('option');
      opt.value = i;
      opt.innerHTML = i;
      if(i == 1){
      opt.selected = "true";
      }
     
      selectDay.appendChild(opt);
  }
}