This eventhandler is called when EmbbeddedWB is about to display a script-error dialogs.
We have several ways to control this event:
1. On the TEmbeddedWB properties, you can find DisabaleErrors section.
One of its sub menus is ScripError. All you need to do is to set it to true (Its default state).

2. You can receive the error-message and other information about the script-error and can determine if you want the dialog to be shown or not. You can also discontinue running of scripts on the page. 

Example:
procedure TfrmMain.EmbeddedWB1ScriptError(Sender: TObject; ErrorLine,
  ErrorCharacter, ErrorCode, ErrorMessage, ErrorUrl: string; var ContinueScript,
  Showdialog: Boolean);
begin
   Edit1.text := ('OnNavigateError '+ ErrorMessage+ '  ' +ErrorCode ); // capture the event details
   Showdialog:= false;  //Do not show the script error dialog
   ContinueScript := true; //Go on loading the page
end;


Notes
1. The easy and fastest way is to set the TEmbeddedWB silent property to true.
I do not recommand to do so because you can miss important messages.:
2. in the DisabaleErrors section ther are 2 more sub items. EnableDDE( disable folder navigation errors) and fpExceptions(disable/enable floating-point exceptions). Its recommended that you will set them both to true.