What is the alternative method of ‘window.external’ in VB Script?

I used the WebBrowser control to add existing Web application written by VB Script code to my Windows Forms client applications.

But, I have some problem. I have to communicate between Web application and Windows Forms applications. I already found similar function in Javascript. ‘window.external’.
I’m looking for the alternative method of ‘window.external’ in VB Script.

please check the following code. how to implement to execute windows Forms Application methods in VB Script?

<script language="vbscript" type="text/vbscript">
   Sub callForm2()
      window.external.ShowMessage("from vbscript")
   End Sub
</script

public class ScriptManager
{
   private Form _form = null;
   public ScriptManager(Form1 form)
   {
      _form = form;
   }


   public void ShowMessage(object msg)
   {
      MessageBox.Show(msg.ToString());
   }
}