CallBackResponse not working all the times

[promi8eas]

I have a TIWAppForm with an TIWLabel (TXTWIDTH) that is updated with the following code:

procedure TIndex.cmdLoginAsyncMouseOver(Sender: TObject; EventParams: TStringList);
var
js: string;
begin
js:='document.getElementById("TXTWIDTH").innerHTML = screen.width;';
WebApplication.CallBackResponse.AddJavaScriptToExecuteAsCDATA(js);
end;

How can I get the value of TXTWIDTH label?