autocompleteextender contextkey problem.

hello

i am trying to set contextkey value by calling SetContextKey function from onkeyup event of textbox.

But i am getting following error

Error    72    The name 'autoCompleteExtender' does not exist in the current context      

function SetContextKey()
    {
    debugger;

        var Date1=document.getElementById('<%=Date1.ClientID %>').value;
        var Date2=document.getElementById('<%=Date2.ClientID %>').value;
      
        $find("<%=autoCompleteExtender.ClientID %>").set_contextKey(Date1+"|"+Date2);
       
        return;
    }

I am not able to find the autocompleteextender in javascript.

-satyajeet