How to a javascript function from c# code behind of Dropdownlist

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ASP.NET

Javascript

C#3.5

Hi,
I need to call two different functions on the dropdownlist's selected index change event.
I have ddl_SelectedIndexChanged event. which binds data to a repeater.
Now I wrote a function which rewrite the url of the page with query string.

What I want is to populate that repeater with the querystring parameter.

What I've tried is, first bind the event to ddl in page_load()

ddl.SelectedIndexChanged+=new EventHandler(ddl_SelectedIndexChanged);

and

if(!Page.IsPostBack)
            {
<pre>ddl.Attributes.Add("onchange", "RedirectURL();  return true;");
}</pre>

For ref.

I am having

protected void ddlBrokerLocation_SelectedIndexChanged(object sender, EventArgs e)
       {
           if (ddlBrokerLocation.SelectedIndex > 0)
           {
               rptRepeater.DataSource = some table;
               rptRepeater.DataBind();

           }
       }

You can see only one function may get called.
In this case "onchange" got called and thus repeater not binded.

Any suggessions please?
Any workaround?