JavaScript function access from plain C++: An example

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Introduction

How can we execute JavaScript functions from C++, a question I asked a long time ago. But, recently, when I needed an interface between a C++ code and a JavaScript function within an HTML page, I decided to code in search of an answer to that question.

Using the code

For this solution, we have a file called "daveWare.html" located in the same directory/path as the *.exe of this program. The JavaScript function in this html page is:

.........

<script type="text/javascript">

function message(messagestring)
{
    alert(messagestring);

}

</script>

........

The solution, just one of many solutions, is to interface the HTML page/document using a COM/ATL interface, the IWebBrowser2 interface within the dWebCtrl class.

With this interface and its method "Navigate", we can navigate URLs and execute JavaScript (using javascript:) codes in the URLs, as follows:

///-///////////////////////////////////////////////////////////////////
///    Execute string "Script"
///-///////////////////////////////////////////////////////////////////
void dWebCtrl::ExecuteScript(char* Script)
{
    BSTR bstrScript;
    BSTR bufferScript;
    static DWORD size=0;
    char nameInput[256]={'\0'};

    memset(nameInput,'\0',sizeof(nameInput)-1);

    wsprintf(nameInput,"javascript:%s",Script);
    
    size = MultiByteToWideChar(CP_ACP, 0, nameInput, -1, 0, 0);
    if (!(bufferScript = 
         (wchar_t *)GlobalAlloc(GMEM_FIXED, sizeof(wchar_t)*size)))
        return;

    MultiByteToWideChar(CP_ACP, 0, nameInput, -1, bufferScript, size);
    bstrScript = SysAllocString(bufferScript);

    SysFreeString(bufferScript);

    pIwb->Navigate(bstrScript, &vEmpty, &vEmpty, &vEmpty, &vEmpty);
    SysFreeString(bstrScript);

    return;
}

That's it. In our main process, we can access any JavaScript function and pass any parameter to it from our C++ code:

///-//////////////////////////////////////////////////////////////
///         Windows Procedure
///-//////////////////////////////////////////////////////////////
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, 
                                  WPARAM wParam, LPARAM lParam)
{

    switch (message)
    /* handle the messages */
    {
        case WM_COMMAND:
            switch LOWORD(wParam)
            {
                case IDM_COMMAND_ALERT:
                    // execute the function "message" with parameter
                    // "David is the best" within the page "daveware.html" called 
                    // in our dWebCtrl
                    WebBrowser.ExecuteScript("javascript:message('David is the best');");
                    break;

                case IDM_FILE_EXIT:
                    SendMessage(hwnd,WM_DESTROY,(WPARAM)0,(LPARAM)0);
                    break;

            }

            break;

        case WM_CREATE:
        {
            GetCurrentDirectory(MAX_PATH-1,szDirectorioTrabajo);

            WebBrowser.Iniciar(hwnd,hInst);
            break;
        }

        case WM_SIZE:

            WebBrowser.OnResize(0,0);
            break;


        case WM_QUIT:
        case WM_DESTROY:
            /* send a WM_QUIT to the message queue */
            PostQuitMessage (0);
            break;


        default:   /* for messages that we don't deal with */
            return DefWindowProc (hwnd, message, wParam, lParam);
    }

    return 0;
}

Now, you can interface your C++ code with any JavaScript function located in any HTML page (you must know how the JavaScript function works, of course). My next step, access JavaScript "var" defined variables from C++. Any advice?

Best regards to all, and good luck with this stuff. My e-mail address. My URL.