How do I call eval() in IE from C++?

Question

With the advent of IE11, IHTMLWindow2::execScript() is deprecated. The recommended approach is to use eval() instead. I\'m automating IE via its C++ COM interfaces, and I ha

Answer 1

I have now verified the eval approach works consistently with IE9, IE10 and IE11 (error checks skipped for breavity):

CComVariant result;
CComDispatchDriver disp = m_htmlWindow; // of IHTMLWindow2
disp.Invoke1(L"eval", &CComVariant(L"confirm('See this?')"), &result);
result.ChangeType(VT_BSTR);
MessageBoxW(V_BSTR(&result));

Feels even better than execScript, because it actually returns the result. It works also in C# with WinForms' WebBrowser:

var result = webBrowser1.Document.InvokeScript("eval", new object[] { "confirm('see this?')" });
MessageBox.Show(result.ToString());

That said, execScript still works for IE11 Preview:

CComVariant result;
m_htmlWindow->execScript(CComBSTR(L"confirm('See this too?')"), CComBSTR(L"JavaScript"), &result);
result.ChangeType(VT_BSTR);
MessageBoxW(V_BSTR(&result));

And it still discards the result, as it always did.

A bit off-topic, but you don't have to stick with eval for this. This approach allows to execute any named method available inside the namespace of the JavaScript window object of the loaded page (via IDispatch interface). You may call your own function and pass a live COM object into it, rather than a string parameter, e.g.:

// JavaScript
function AlertUser(user)
{
  alert(user.name);
  return user.age;
}

// C++
CComDispatchDriver disp = m_htmlWindow; // of IHTMLWindow2
disp.Invoke1(L"AlertUser", &CComVariant(userObject), &result);

I'd prefer the above direct call to eval where possible.

[EDITED]

It takes some tweaks to make this approach work for out-of-process calls. As @JimEvans pointed out in the comments, Invoke was returning error 0x80020006 ("Unknown name"). However, a test HTA app worked just fine, what made me think to try IDispatchEx::GetDispId for name resolution. That indeed worked (error checks skipped):

CComDispatchDriver dispWindow;
htmlWindow->QueryInterface(&dispWindow);

CComPtr<IDispatchEx> dispexWindow;
htmlWindow->QueryInterface(&dispexWindow);

DISPID dispidEval = -1;
dispexWindow->GetDispID(CComBSTR("eval"), fdexNameCaseSensitive, &dispidEval);
dispWindow.Invoke1(dispidEval, &CComVariant("function DoAlert(text) { alert(text); }")); // inject

DISPID dispidDoAlert = -1;
dispexWindow->GetDispID(CComBSTR("DoAlert"), fdexNameCaseSensitive, &dispidDoAlert) );
dispWindow.Invoke1(dispidDoAlert, &CComVariant("Hello, World!")); // call

The full C++ test app is here: http://pastebin.com/ccZr0cG2

[UPDATE]

This update creates __execScript method on a window object of a child iframe, out-of-proc. The code to be injected was optimized to return the target window object for later use (no need to make a series of out-of-proc calls to obtain the iframe object, it's done in the context of the main window):

CComBSTR __execScriptCode(L"(window.__execScript = function(exp) { return eval(exp); }, window.self)");

Below is the code for C++ console app (pastebin), some error checks skipped for breavity. There's also a corresponding prototype in .HTA, which is more readable.

//
// http://stackoverflow.com/questions/18342200/how-do-i-call-eval-in-ie-from-c/18349546//
//

#include <tchar.h>
#include <ExDisp.h>
#include <mshtml.h>
#include <dispex.h>
#include <atlbase.h>
#include <atlcomcli.h>

#define _S(a) \
    { HRESULT hr = (a); if (FAILED(hr)) return hr; } 

#define disp_cast(disp) \
    ((CComDispatchDriver&)(void(static_cast<IDispatch*>(disp)), reinterpret_cast<CComDispatchDriver&>(disp)))

struct ComInit {
    ComInit() { ::CoInitialize(NULL); }
    ~ComInit() { CoUninitialize(); }
};

int _tmain(int argc, _TCHAR* argv[])
{
    ComInit comInit;

    CComPtr<IWebBrowser2> ie;
    _S( ie.CoCreateInstance(L"InternetExplorer.Application", NULL, CLSCTX_LOCAL_SERVER) );
    _S( ie->put_Visible(VARIANT_TRUE) );
    CComVariant ve;
    _S( ie->Navigate2(&CComVariant(L"http://jsfiddle.net/"), &ve, &ve, &ve, &ve) );

    // wait for page to finish loading
    for (;;)
    {
        Sleep(250);
        READYSTATE rs = READYSTATE_UNINITIALIZED;
        ie->get_ReadyState(&rs);
        if ( rs == READYSTATE_COMPLETE )
            break;
    }

    // inject __execScript into the main window

    CComPtr<IDispatch> dispDoc;
    _S( ie->get_Document(&dispDoc) );
    CComPtr<IHTMLDocument2> htmlDoc;
    _S( dispDoc->QueryInterface(&htmlDoc) );
    CComPtr<IHTMLWindow2> htmlWindow;
    _S( htmlDoc->get_parentWindow(&htmlWindow) );
    CComPtr<IDispatchEx> dispexWindow;
    _S( htmlWindow->QueryInterface(&dispexWindow) );

    CComBSTR __execScript("__execScript");
    CComBSTR __execScriptCode(L"(window.__execScript = function(exp) { return eval(exp); }, window.self)");

    DISPID dispid = -1;
    _S( dispexWindow->GetDispID(CComBSTR("eval"), fdexNameCaseSensitive, &dispid) );
    _S( disp_cast(dispexWindow).Invoke1(dispid, &CComVariant(__execScriptCode)) ); 

    // inject __execScript into the child frame

    WCHAR szCode[1024];
    wsprintfW(szCode, L"document.all.tags(\"iframe\")[0].contentWindow.eval(\"%ls\")", __execScriptCode.m_str);

    dispid = -1;
    _S( dispexWindow->GetDispID(__execScript, fdexNameCaseSensitive, &dispid) );
    CComVariant vIframe;
    _S( disp_cast(dispexWindow).Invoke1(dispid, &CComVariant(szCode), &vIframe) ); // inject __execScript and return the iframe's window object
    _S( vIframe.ChangeType(VT_DISPATCH) );

    CComPtr<IDispatchEx> dispexIframe;
    _S( V_DISPATCH(&vIframe)->QueryInterface(&dispexIframe) );

    dispid = -1;
    _S( dispexIframe->GetDispID(__execScript, fdexNameCaseSensitive, &dispid) );
    _S( disp_cast(dispexIframe).Invoke1(dispid, &CComVariant("alert(document.URL)")) ); // call the code inside child iframe

    return 0;
}