I am having problem on how to load the HTML <select> with values whenever the page is first loaded or when refreshed.

I am actually trying to create a date_select with 3 dropdown menus which includes year, month, and days in which when the month-menu or year-menu is changed it will automatically adjust the number of days.

For example, when I selected the month March the days will be 31 or April the days will be 30 only.

My problem is when the page is first loaded the day-menu is empty. I tried onload on the <select> but it didn't work. I am a beginner in programming so I am having trouble even simple exercises like this. Please help.

date_select.php

<script type=text/javascript >



 function loadDays() {

  var year = parseInt(document.getElementById('years').value);

  var month = document.getElementById('months').value;

  var months = new Array(January, February, March, April, May, June, July, August, September, October, November, December);

  var days = new Array(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);



  if ((year % 4) == 0)  days[1] = 29;



  var days_select = document.getElementById('days');

  days_select.options.length = 0;



  for(i in months) {

   if (month == months[i]) {

    for(var j = 1; j <= days[i]; j++ ) days_select.options[days_select.options.length] = new Option(j, j);

    break;

   }

  }

 }



</script>



<span style=display: table; >

 <span style=display: table-cell; >

  <select id=years onchange=loadDays();>

   <?php 

    for($year = 1900; $year <= 2100; $year++ ) {

     if ($year == date('Y')) echo <option value='$year' selected=''> . $year . </option>;

     else echo <option value='$year'> . $year . </option>;

    }

   ?>

  </select>

 </span>

 &nbsp;

 <span style=display: table-cell; >

  <select id=months onchange=loadDays();>

   <?php 

    $months = array(January, February, March, April, May, June, July, August, September, October, November, December );



    foreach($months as $month){

     if ($month == date('M')) echo <option value='$month' selected=''>  . $month . </option>;

     else echo <option value='$month'>  . $month . </option>;

    }

   ?>

  </select>

 </span>

 &nbsp;

 <span style=display: table-cell; >

  <select id=days onload=loadDays();>



  </select>

 </span>

</span>