why this code work fine
function OnChangeAction()
{
    var e = document.getElementById('<%=ddlSelectItems.ClientI  D %>');  
    var selVal = e.options[e.selectedIndex].value; 
    SelectAll(selVal);
}
and this code not work
function OnChangeAction()
{    
    var selVal = $("id$=ddlSelectItems option:selected").text();
    SelectAll(selVal);
}
<asp

ropDownList ID="ddlSelectItems" runat="server"                         
onchange="OnChangeAction();">                        
</asp

ropDownList>
SelectAll function work fine.