js method to dynamically add drop-down box data source to textbox_javascript skills

$("#<%=lstCarBrand.ClientID%>" ).change(function () {
$("#<%=txtCarSeries.ClientID%>").val("");//Clear the text box
$("#<%= txtCarSeries.ClientID%>").unautocomplete();//Clear autocomplete
$("#<%=txtCarSeries.ClientID%>").autocomplete('Ajax/AjaxCusCarEssentialVersion.aspx', {// Add autocomplete
width: 200,
multiple: false,
matchContains: true,
extraParams: {//Parameters passed
"CarBrand": function () {
return $ ("#<%=lstCarBrand.ClientID%>").val();
}
}
});
});