Javascript injection in Internet Explorer, returns null

Question

I am developing an application that performs automation in internet explorer, I am using the Shdocvw to do this.

My problem is I can’t get the return of an injection of Javascript

public static void wJScript(string script) {
  try {
    Thread th = new Thread(ExecuteJavaScriptWorker);
    th.SetApartmentState(ApartmentState.STA);
    th.Start(script);
  }
  catch (Exception) {
    throw;
  }
}

private static void ExecuteJavaScriptWorker(object script) {
  try {         
    IHTMLDocument2 document = IE.Document;
    object resp = document.parentWindow.execScript(script.ToString(), "JScript");
    Console.Write(resp);
  }
  catch (Exception) {
    throw;
  }
}

My variable Resp always returns null

The variable script can receive any Javascript command from a single document.getElementById('id').value even call a function I have on the page:

Let’s say I have following function on my page:

function soma(a,b) {
  return a + b;
}

And pass as parameter to my function wJScript("soma(1,2)") it should return me the result of the function, but this does not occur!

Answer 1

This is what is expected from this method.

In accordance with the documentation the method execScript always returns null

See an excerpt:

This method Always Returns null.

How translated is:

This method always returns null

Answer 2

Test this section and see if it generates any exception

       try{
          IHTMLDocument2 doc = (IHTMLDocument2)IE.Document;

            if (doc != null){
                IHTMLWindow2 parentWindow = doc.parentWindow;
                if (parentWindow != null)
                    parentWindow.execScript(script, "javascript");
             }
        }
        catch(Exception ex) {
        }