Using Javascript to Call C++ in Internet Explorer

Question

I have seen this for BHO extensions, where the JavaScript can call functions in the C++ BHO. But lets say I am not using a BHO, instead I have a C++ console application that creates an IE COM object like so:

HRESULT hr = CoCreateInstance(
            CLSID_InternetExplorer,
            NULL,
            CLSCTX_LOCAL_SERVER,
            IID_IWebBrowser2,
            (void**)&_cBrowser);

I also have a class which "owns" the IWebBrowser2 object that comes back from this function.

class BrowserWrapper{
    public: 
        CComPtr<IWebBrowser2> pBrowser;

        void SomeFunction(...)
}

Is there a way to call a function like "SomeFunction" in the wrapper class from the JavaScript in the spawned IWebBrowser2 object?

Answer 1

You must implement the IDocHostUIHandler interface and set it to the web browser with a code similar to this (extracted from the doc):

ComPtr<IDispatch> spDocument;
hr = spWebBrowser2->get_Document(&spDocument);
if (SUCCEEDED(hr) && (spDocument != nullptr))
{
    // Request default handler from MSHTML client site
    ComPtr<IOleObject> spOleObject;
    if (SUCCEEDED(spDocument.As(&spOleObject)))
    {
        ComPtr<IOleClientSite> spClientSite;
        hr = spOleObject->GetClientSite(&spClientSite);
        if (SUCCEEDED(hr) && spClientSite)
        {
            // Save pointer for delegation to default 
            m_spDefaultDocHostUIHandler = spClientSite;
        }
    }

    // Set the new custom IDocHostUIHandler
    ComPtr<ICustomDoc> spCustomDoc;
    if (SUCCEEDED(spDocument.As(&spCustomDoc)))
    {
        // NOTE: spHandler is user-defined class
        spCustomDoc->SetUIHandler(spHandler.Get());
    }
} 

You must specifically implement the GetExternal method

Now, in IE's javascript (or vbscript for that matter), you can access your host with a call like this:

var ext = window.external; // this will call your host's IDocHostUIHandler.GetExternal method
ext.SomeFunction(...); // implemented by your object

What you return in GetExternal must be an IDispatch object that you can design the way you want.