How to execute a Javascript function in a Webbrowser/ IE Document

uses
  MSHTML_TLB, SHDocVw, ShellAPI;

// function to execute a script function

function ExecuteScript(doc: IHTMLDocument2; script: string; language: string): Boolean;
var
  win: IHTMLWindow2;
  Olelanguage: Olevariant;
begin
  if doc <> nil then
  begin
    try
      win := doc.parentWindow;
      if win <> nil then
      begin
        try
          Olelanguage := language;
          win.ExecScript(script, Olelanguage);
        finally
          win := nil;
        end;
      end;
    finally
      doc := nil;
    end;
  end;
end;

procedure FillInGMXForms(WB: ShDocVW_TLB.IWebbrowser2; IDoc1: IHTMLDocument2;
  Document: Variant; AKennung, APasswort: string);
const
  IEFields: array[1..4] of string = ('INPUT', 'text', 'INPUT', 'password');
var
  IEFieldsCounter: Integer;
  i: Integer;
  m: Integer;
  ovElements: OleVariant;
begin
  if Pos('GMX - Homepage', Document.Title) <> 0 then

    while WB.ReadyState <> READYSTATE_COMPLETE do
      Application.ProcessMessages;

  // count forms on document and iterate through its forms
  IEFieldsCounter := 0;
  for m := 0 to Document.forms.Length - 1 do
  begin
    ovElements := Document.forms.Item(m).elements;

    // iterate through elements
    for i := ovElements.Length - 1 downto 0 do
    begin
      try
        // if input fields found, try to fill them out
        if (ovElements.item(i).tagName = IEFields[1]) and
          (ovElements.item(i).type = IEFields[2]) then
        begin
          ovElements.item(i).Value := AKennung;
          Inc(IEFieldsCounter);
        end;

        if (ovElements.item(i).tagName = IEFields[3]) and
          (ovElements.item(i).type = IEFields[4]) then
        begin
          ovElements.item(i).Value := APasswort;
          Inc(IEFieldsCounter);
        end;
      except
        // failed...
      end;
    end; { for i...}
  end;  { for m }
  // if the fields are filled in, submit.
  if IEFieldsCounter = 3 then ExecuteScript(iDoc1, 'document.login.submit()',
      'JavaScript');
end;

function LoginGMX_IE(AKennung, APasswort: string): Boolean;
var
  ShellWindow: IShellWindows;
  WB: ShDocVW_TLB.IWebbrowser2;
  spDisp: IDispatch;
  IDoc1: IHTMLDocument2;
  Document: Variant;
  k: Integer;
begin
  ShellWindow := CoShellWindows.Create;
  // get the running instance of Internet Explorer
  for k := 0 to ShellWindow.Count do
  begin
    spDisp := ShellWindow.Item(k);
    if spDisp = nil then Continue;
    // QueryInterface determines if an interface can be used with an object
    spDisp.QueryInterface(iWebBrowser2, WB);
    if WB <> nil then
    begin
      WB.Document.QueryInterface(IHTMLDocument2, iDoc1);
      if iDoc1 <> nil then
      begin
        WB := ShellWindow.Item(k) as ShDocVW_TLB.IWebbrowser2;
        Document := WB.Document;
        // if GMX page...
        FillInGMXForms(WB, IDoc1, Document, AKennung, APasswort);
      end;  { idoc <> nil }
    end; { wb <> nil }
  end;  { for k }
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  ShellExecute(Handle,
    'open',
    'http://www.gmx.ch',
    nil,
    nil,
    SW_SHOW);
  Sleep(2000);
  LoginGMX_IE('user@gmx.net', 'pswd');
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  IDoc1: IHTMLDocument2;
  Web: ShDocVW_TLB.IWebBrowser2;
begin
  Webbrowser1.Navigate('http://www.gmx.ch');
  while Webbrowser1.ReadyState <> READYSTATE_COMPLETE do
    Application.ProcessMessages;
  Webbrowser1.Document.QueryInterface(IHTMLDocument2, iDoc1);
  Web := WebBrowser1.ControlInterface;
  FillInGMXForms(Web, iDoc1, Webbrowser1.Document, 'user@gmx.net', 'pswd');
end;