Add Options to a Combo Box Using JavaScript

You can use a JavaScript function to modify the options available in a pull-down box on the page.

The following example adds a new blank selection at the top of the starthour field at Level 2:

function changeStartHour()
 {
   try
   {
       document.forms[0].starthour.add(new Option("", "", true, true), document.forms[0].starthour.options[0])
   }
   catch(e)
   { //in IE, try the below version instead of add()
       document.forms[0].starthour.add(new Option("", "", true, true), 0)
   }
}
changeStartHour();

The options available are:

document.forms[0].starthour.add(new Option(Display text, Store value, defaultSelected, selected), document.forms[0].starthour.options[0])