CallBackResponse not working all the times

[promi8eas]

Please I need to execute some javascript commands in my project. I found that the CallBackResponse can do the job.
The issue I face is that the procedure is not working all the times.

The first example which i want to focus to a text box is working perfectly.
var
  js: string;
begin
  js := 'document.getElementById("TXTQUANTITY").focus();';
  WebApplication.CallBackResponse.AddJavaScriptToExecuteAsCDATA(js);
end;


but when i try to run other commands it does nothing even a simple pop message
  js:=  'windows.alert("I am an alert box!");';
  WebApplication.CallBackResponse.AddJavaScriptToExecute(js);

Is there something else I have to pay attention.

i am running XE6 and Intraweb 14.0.50 version