Browser Helper Object to execute JavaScript in Internet Explorer 11

Question

I've scoured the web for examples of a Browser Helper object that executes JS and have gotten this far but the JS doesn't seem to execute. Code is below and I've also run regasm.exe codebase/ on the dll but nothing seems to happen when I load the extension in the browser - any suggestions?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using SHDocVw;
using mshtml;
using System.IO;
using Microsoft.Win32;
using System.Runtime.InteropServices;

namespace My_BHO
{
    [ComVisible(true), InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid("FC4801A3-2BA9-11CF-A229-00AA003D7352")]
    public interface IObjectWithSite
    {
        [PreserveSig]
        int SetSite([MarshalAs(UnmanagedType.IUnknown)] object site);

        [PreserveSig]
        int GetSite(ref Guid guid, out IntPtr ppvSite);
    }
    [
        ComVisible(true),
        Guid("2159CB25-EF9A-54C1-B43C-E30D1A4A8277"),
        ClassInterface(ClassInterfaceType.None)
    ]

    public class BHO : IObjectWithSite
    {
        private WebBrowser webBrowser;
        public const string BHO_REGISTRY_KEY_NAME = "Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Browser Helper Objects";

        public int SetSite(object site)
        {
            if (site != null)
            {
                webBrowser = (WebBrowser)site;
                webBrowser.DocumentComplete += new DWebBrowserEvents2_DocumentCompleteEventHandler(this.OnDocumentComplete);
            }
            else
            {
                webBrowser.DocumentComplete -= new DWebBrowserEvents2_DocumentCompleteEventHandler(this.OnDocumentComplete);
                webBrowser = null;
            }
            return 0;
        }

        public int GetSite(ref Guid guid, out IntPtr ppvSite)
        {
            IntPtr punk = Marshal.GetIUnknownForObject(webBrowser);
            int hr = Marshal.QueryInterface(punk, ref guid, out ppvSite);
            Marshal.Release(punk);
            return hr;
        }

        public void OnDocumentComplete(object pDisp, ref object URL)
        {
            HTMLDocument document = (HTMLDocument)webBrowser.Document;
            IHTMLElement head = (IHTMLElement)((IHTMLElementCollection)document.all.tags("head")).item(null, 0);
            IHTMLScriptElement adaptiveScript = (IHTMLScriptElement)document.createElement("script");
            adaptiveScript.type = @"text/javascript";
            adaptiveScript.text = "alert('hi');";
            ((HTMLHeadElement)head).appendChild((IHTMLDOMNode)adaptiveScript);
        }

        [ComRegisterFunction]
        public static void RegisterBHO(Type type)
        {
            RegistryKey registryKey = Registry.LocalMachine.OpenSubKey(BHO_REGISTRY_KEY_NAME, true);
            if (registryKey == null) registryKey = Registry.LocalMachine.CreateSubKey(BHO_REGISTRY_KEY_NAME);

            string guid = type.GUID.ToString("B");
            RegistryKey ourKey = registryKey.OpenSubKey(guid, true);
            if (ourKey == null) ourKey = registryKey.CreateSubKey(guid);
            ourKey.SetValue("NoExplorer", 1, RegistryValueKind.DWord);

            registryKey.Close();
            ourKey.Close();
        }

        [ComUnregisterFunction]
        public static void UnregisterBHO(Type type)
        {
            RegistryKey registryKey = Registry.LocalMachine.OpenSubKey(BHO_REGISTRY_KEY_NAME, true);
            string guid = type.GUID.ToString("B");
            if (registryKey != null) registryKey.DeleteSubKey(guid, false);
        }
    }

}

I've mainly been trying to follow this tutorial but would appreciate any other more recent examples! https://www.codeproject.com/Articles/149258/Inject-HTML-and-JavaScript-into-an-existing-page-w

Maybe something with the GUIDs is off?

Thanks in advance!