Here is some code to run a javascript function on the client side when a value changes in a drop down box. In this case I have a list of dates populating a drop down box. When the date changes the value of a DIV section changes to a corresponding end date.

In the appSetting section of the web.config file:

<add key=“StartDates“ value=“12/06/06, 02/27/07, 05/09/07, 07/03/07, 10/10/07, 01/08/08, 03/02/08“/>
<add key=“EndDates“ value=“10/08/07, 12/21/07, 03/18/08, 05/29/08, 08/18/08, 10/29/08, 01/27/09“/>

In the page load section:

 ‘ Get the start and end dates from the web.config file
 
 Dim StartDates As Array
 StartDates = ConfigurationManager.AppSettings(“StartDates”).Split(“,”)
 EndDates = “‘” & ConfigurationManager.AppSettings(“EndDates”).Replace(“, “, “‘, ‘”) & “‘”  ‘ format the string for a javascript array
 EndDate = EndDates.Substring(0, EndDates.IndexOf(“,”)).Replace(“‘”, “”)
 
 ‘ Populate the Start Date drop down / combo box
 
 ddlStartDate.AppendDataBoundItems = True
 Dim Item As String
 For Each Item In StartDates
  Items = New ListItem
  Items.Text = Item
  Items.Value = Item
  ddlStartDate.Items.Add(Items)
 Next
 
 ‘ Register the javascript code to run on the client side
 
 ddlStartDate.Attributes.Add(“onchange”, “javascript: doAction(” + ddlStartDate.ClientID + “)”)

Then in the web form:

<table border =”0″><tr><td><asp:DropDownList ID=”ddlStartDate” runat=”server”></asp:DropDownList></td><td><div id=”EstCompDate”>Est. Comp. Date: <b><%=EndDate%></b></div></td></tr></table>

Then at the bottom of the HTML of the page (just above the </html> tag):

<script language=”javascript”>
var endDates = new Array(<%=EndDates %>);
function doAction(id) {
   var selection = id.options[id.selectedIndex].value;
   EstCompDate.innerHTML = ‘Est. Comp. Date: <b>’ + endDates[id.selectedIndex] + ‘</b>’;
}
</script>