显示日期，月份和年份代替当前的日期，月份和年份

Question

我有以下JavaScript代码，它在下拉菜单中显示当天，月份和年份。代码如下：

var monthtext=['January','February','March','April','May','June','July','August','September','October','November','December']; 

function populatedropdown(dayfield, monthfield, yearfield) { 
    var today=new Date() 
    var dayfield=document.getElementById(dayfield) 
    var monthfield=document.getElementById(monthfield) 
    var yearfield=document.getElementById(yearfield) 
    for (var i=0; i<31; i++) { 
     dayfield.options[i]=new Option(i+1) 
    } 
    dayfield.options[today.getDate()]=new Option(today.getDate(), today.getDate(), true, true) //select today's day 
    for (var m=0; m<12; m++) { 
     monthfield.options[m]=new Option(monthtext[m], monthtext[m]) 
    } 
    monthfield.options[today.getMonth()]=new Option(monthtext[today.getMonth()], monthtext[today.getMonth()], true, true) //select today's month 
    var thisyear=today.getFullYear() 
    for (var y = 0; y < 100; y++) { 
     yearfield.options[y] = new Option(thisyear, thisyear) 
     thisyear -= 1 
    } 
    yearfield.options[0]=new Option(today.getFullYear(), today.getFullYear(), true, true) //select today's year 
} 

<script type="text/javascript"> 
//populatedropdown(id_of_day_select, id_of_month_select, id_of_year_select) 
window.onload=function(){ 
populatedropdown("daydropdown", "monthdropdown", "yeardropdown") 
} 
</script> 



<select id="daydropdown" name="D-DOB"></select> 
    <select id="monthdropdown" name="M-DOB"></select> 
    <select id="yeardropdown" name="Y-DOB"></select> 

我想显示“选择日”，“选择月”，并在地方像电流值的“选择年份”为默认值：

<option value="">Select Day</option> 

小提琴： https://jsfiddle.net/u2m243qf/1/

编辑：

由我自己解决：

我重构了我的代码，并得到了一个更简单的解决方案。新的小提琴： https://jsfiddle.net/u2m243qf/9/

Answer 1

如果我理解了您的要求，您希望在选项中显示默认值？如果是这样，只是做：

<option value="x" selected="your-selected"> Select day </option> 

您也可以找到关于该主题在这里一个更深入的讨论： How can I set the default value for an HTML <select> element?

...在JS是：

dayfield.value = "Select Day";