JS in the head of your document:
1 2 <script language="JavaScript" type="text/javascript"> 3 function entrydate() 4 { 5 var month = document.entryform.start_month.value; 6 var day = document.entryform.start_day.value; 7 var year = document.entryform.start_year.value; 8 var time = document.entryform.start_time.value; 9 document.entryform.entry_date.value = year+month+day+" "+time; 10 } 11 </script>
Code for the actual fields:
1 2 <!-- Begin Month --> 3 <select name="start_month" onchange="entrydate();"> 4 <option value="01-" >January</option> 5 <option value="02-" >February</option> 6 <option value="03-" >March</option> 7 <option value="04-" >April</option> 8 <option value="05-" >May</option> 9 10 <option value="06-" >June</option> 11 <option value="07-" >July</option> 12 <option value="08-" selected>August</option> 13 <option value="09-" >September</option> 14 <option value="10-" >October</option> 15 <option value="11-" >November</option> 16 <option value="12-" >December</option> 17 18 </select> 19 <!-- End Month --> 20 21 <!-- Begin Day --> 22 <select name="start_day" onchange="entrydate();"> 23 <option value="1" >1</option> 24 <option value="2" >2</option> 25 <option value="3" >3</option> 26 <option value="4" >4</option> 27 <option value="5" >5</option> 28 <option value="6" >6</option> 29 <option value="7" >7</option> 30 <option value="8" >8</option> 31 32 <option value="9" >9</option> 33 <option value="10" >10</option> 34 <option value="11" >11</option> 35 <option value="12" >12</option> 36 <option value="13" >13</option> 37 <option value="14" >14</option> 38 <option value="15" >15</option> 39 <option value="16" >16</option> 40 <option value="17" >17</option> 41 42 <option value="18" >18</option> 43 <option value="19" >19</option> 44 <option value="20" >20</option> 45 <option value="21" >21</option> 46 <option value="22" >22</option> 47 <option value="23" >23</option> 48 <option value="24" >24</option> 49 <option value="25" >25</option> 50 <option value="26" >26</option> 51 52 <option value="27" >27</option> 53 <option value="28" >28</option> 54 <option value="29" >29</option> 55 <option value="30" selected>30</option> 56 <option value="31" >31</option> 57 58 </select> 59 <!-- End Day --> 60 <!-- Begin Year --> 61 <select name="start_year" onchange="entrydate();"> 62 <option value="2005-" >2005</option> 63 64 <option value="2006-" selected>2006</option> 65 <option value="2007-" >2007</option> 66 67 </select> 68 <!-- End Year --> 69 <!-- Begin Time --> 70 <select name="start_time" onchange="entrydate();"> 71 <option value="6:00 AM" >6:00 AM</option> 72 <option value="6:30 AM" >6:30 AM</option> 73 <option value="7:00 AM" >7:00 AM</option> 74 <option value="7:30 AM" >7:30 AM</option> 75 76 <option value="8:00 AM" selected>8:00 AM</option> 77 <option value="8:30 AM" >8:30 AM</option> 78 <option value="9:00 AM" >9:00 AM</option> 79 <option value="9:30 AM" >9:30 AM</option> 80 <option value="10:00 AM" >10:00 AM</option> 81 <option value="10:30 AM" >10:30 AM</option> 82 <option value="11:00 AM" >11:00 AM</option> 83 <option value="11:30 AM" >11:30 AM</option> 84 <option value="12:00 PM" >12:00 PM</option> 85 86 <option value="12:30 PM" >12:30 PM</option> 87 <option value="1:00 PM" >1:00 PM</option> 88 <option value="1:30 PM" >1:30 PM</option> 89 <option value="2:00 PM" >2:00 PM</option> 90 <option value="2:30 PM" >2:30 PM</option> 91 <option value="3:00 PM" >3:00 PM</option> 92 <option value="3:30 PM" >3:30 PM</option> 93 <option value="4:00 PM" >4:00 PM</option> 94 <option value="4:30 PM" >4:30 PM</option> 95 96 <option value="5:00 PM" >5:00 PM</option> 97 <option value="5:30 PM" >5:30 PM</option> 98 <option value="6:00 PM" >6:00 PM</option> 99 <option value="6:30 PM" >6:30 PM</option> 100 <option value="7:00 PM" >7:00 PM</option> 101 <option value="7:30 PM" >7:30 PM</option> 102 <option value="8:00 PM" >8:00 PM</option> 103 <option value="8:30 PM" >8:30 PM</option> 104 <option value="9:00 PM" >9:00 PM</option> 105 106 <option value="9:30 PM" >9:30 PM</option> 107 <option value="10:00 PM" >10:00 PM</option> 108 <option value="10:30 PM" >10:30 PM</option> 109 <option value="11:00 PM" >11:00 PM</option> 110 <option value="11:30 PM" >11:30 PM</option> 111 112 </select> 113 <!-- End Time --> 114 <input type="hidden" name="entry_date" value="2006-08-30 8:57 AM" />
Full credit for this goes to Solspace!