JavaScript call from C++

• Download demo project - 33 Kb
• Download source - 3 Kb

Introduction

Sometimes when we are using the IE Browser Control inside of a C++ application you need to get access to the HTML elements. We can do it by using standard COM objects like IWebBrowser2, IHTMLDocument2, etc. By this method we can easy implement features like click button, click anchor, get input string, get HTML text, etc. Unfortunately, Microsoft did not provide similar objects for JavaScript. At any case to make a control for the JavaScript object inside of HTML page it is possible by using traditional COM approach. This article describes the class CWebPage which allows to do it and technique to call Java Script Function from C++ code.

How to do

As the result of using presented class it will be easy to call any JavaScript function from C++ code. For implement this feature we should to get pointer to the IHTMLDocument2 interface. If we are using CHtmlView class from MFC we can get one by using member function CHtmlView::GetHtmlDocument(). In case of using IWebBrowser or IWebBrowser2 components the function get_Document will bring us desired interface. Here is example:

CComPtr<IDispatch> spDisp = CHtmlView::GetHtmlDocument();
m_webPage.SetDocument(spDisp);

The rest of all things will be done by CWebPage class. Here is example of JavaScript call without parameters.

m_webPage.CallJScript("Welcome");

The example of the JavaScript call with 2 parameters will looks like here.

m_webPage.CallJScript("Miltiply","2.34","3.32");

The Class Implementation

class CWebPage
{
public:
  CWebPage();
  virtual ~CWebPage();

  bool SetDocument(IDispatch* pDisp);
  LPDISPATCH GetHtmlDocument() const;
  const CString GetLastError() const;
  bool GetJScript(CComPtr<IDispatch>& spDisp);
  bool GetJScripts(CComPtr<IHTMLElementCollection>& spColl);
  CString ScanJScript(CString& strAText,CStringArray& args);

  bool CallJScript(const CString strFunc);
  bool CallJScript(const CString strFunc,const CString strArg1);
  bool CallJScript(const CString strFunc,const CString strArg1,
                   const CString strArg2);
  bool CallJScript(const CString strFunc,const CString strArg1,
                   const CString strArg2,const CString strArg3);
  bool CallJScript(const CString strFunc,const CStringArray& paramArray);

protected:

  CComPtr<IHTMLDocument2> m_spDoc;

};

Calling Technique

The mentioned above technique splits on the following steps: 

• Getting pointer to the IHTMLDocument2 interface. 
• Getting IDispatch for JavaScript object in HTML document 
• Getting DISPID for given name of JavaScript function 
• Putting parameters to DISPPARAM structure
• Calling JavaScript function by using Invoke method of IDispatch interface

Here is example of getting IDispatch pointer to the Java Scripts objects

bool CWebPage::GetJScript(CComPtr<IDispatch>& spDisp)
{
  HRESULT hr = m_spDoc->get_Script(&spDisp);
  ATLASSERT(SUCCEEDED(hr));
  return SUCCEEDED(hr);
}

And here is final function to call Java Script

CComVariant CWebPage::CallJScript(const CString strFunc,
                                  const CStringArray& paramArray)
{
  //Getting IDispatch for Java Script objects

  CComPtr<IDispatch> spScript;
  if(!GetJScript(spScript))
  {
    ShowError("Cannot GetScript");
    return false;
  }
  //Find dispid for given function in the object

  CComBSTR bstrMember(strFunc);
  DISPID dispid = NULL;
  HRESULT hr = spScript->GetIDsOfNames(IID_NULL,&bstrMember,1,
                            LOCALE_SYSTEM_DEFAULT,&dispid);
  if(FAILED(hr))
  {
    ShowError(GetSystemErrorMessage(hr));
    return false;
  }
  
  const int arraySize = paramArray.GetSize();
  //Putting parameters  

  DISPPARAMS dispparams;
  memset(&dispparams, 0, sizeof dispparams);
  dispparams.cArgs      = arraySize;
  dispparams.rgvarg     = new VARIANT[dispparams.cArgs];
  dispparams.cNamedArgs = 0;
  
  for( int i = 0; i < arraySize; i++)
  {
    CComBSTR bstr = paramArray.GetAt(arraySize - 1 - i); // back reading

    bstr.CopyTo(&dispparams.rgvarg[i].bstrVal);
    dispparams.rgvarg[i].vt = VT_BSTR;
  }
  EXCEPINFO excepInfo;
  memset(&excepInfo, 0, sizeof excepInfo);
  CComVariant vaResult;
  UINT nArgErr = (UINT)-1;  // initialize to invalid arg

  //Call JavaScript function         

  hr = spScript->Invoke(dispid,IID_NULL,0,
                        DISPATCH_METHOD,&dispparams,
                        &vaResult,&excepInfo,&nArgErr);
  delete [] dispparams.rgvarg;
  if(FAILED(hr))
  {
    ShowError(GetSystemErrorMessage(hr));
    return false;
  }
  return vaResult;
}

Notes About the Demo

To call a JavaScript function from the demo you should select function in the tree in the left window. After this press the "!" button on the menu bar.

You must Sign In to use this message board.

FAQ    Noise Tolerance Very HighHighMediumLowVery Low   Layout Expand Posts & RepliesThread ViewNo JavascriptNo JS + Preview   Per page 102550

Msgs 1 to 25 of 59 (Total in Forum: 59) (Refresh) FirstPrevNext

What about cross-platform? ComaWhite86 23:33 13 Dec '08   What about without any Microsoft api? for cross-platform? Sign In·View Thread·PermaLink calling java from c++ kioo0509 18:14 3 Oct '08   How to use c++ to call java funtion?? Has the model program to be possible to refer? THX Sign In·View Thread·PermaLink Hi can anybody help me srinileo 16:46 23 Sep '08   How to run servlet program in apache tomcat server and how to run jsp in weblogic server. If u have any document u can send to srinileo_be@yahoo.com. Sign In·View Thread·PermaLink IHTMLDocument without window Muran 1:52 26 Aug '08   Hi all! I have a problem with calling js function when there is no windows associated with IHTMLDocument.. idea is to 1. create htmldoc m_ptrJSContainer.CoCreateInstance( CLSID_HTMLDocument ); 2. load jScipt inside Load into IStream of m_ptrJSContainer 3. and then call function GetIDsOfNames return "Unknown name" if called immediately after loading. and ITypeInfo contains only one item with the strange name "item". google doesn't know the answer.. Sign In·View Thread·PermaLink 2.00/5 (1 vote) Re: IHTMLDocument without window Muran 3:27 26 Aug '08   After searching i found the key. The problem is that html is not loaded immediatly.. So I just processing message queue until readyState != complete. using the next function bool ProcessMessage() { MSG msg; BOOL res = PeekMessage( &msg, 0, 0, 0, PM_NOREMOVE); if( !res || ( WM_QUIT == msg.message ) ) return false; TranslateMessage(&msg); DispatchMessage(&msg); PeekMessage( &msg, 0, 0, 0, PM_REMOVE); return true; } this solution is not ideal, but I don't have any other Sign In·View Thread·PermaLink How to call external JavaScript ? naren_code 5:48 21 Jun '07   Hi, Your code to call script function is really great. It gave me points for development. But now I am stuck up with new problem. I want to call external javascript function which is being accessed by same html page? How can we access it? Any help would be really great..... regards, narendra. Sign In·View Thread·PermaLink 1.75/5 (4 votes) Re: How to call external JavaScript ? bumbumtrack 20:52 2 Jul '07   Hi Naren, Will you please post some code that how TO get pointer to the IHTMLDocument2 interface. I am a new one to COM and do not know anything in it. I just tried to include the WebPage.h and WebPage.cpp in my project and added follwing lines in my project, but its not working. CComPtr spDisp = CHtmlView::GetHtmlDocument(); m_webPage.SetDocument(spDisp); I tried to contact the author but I am not getting any response from him. Will you please post some code which will call a Javascript using this class. Thanks in advance, laxman_jadhav@yahoo.com Sign In·View Thread·PermaLink 1.64/5 (6 votes) support for firefox vikram1979 5:04 8 Aug '06   just curious if firefox / netscape will also be supported or not? with my limited knowledge, i know that one can write netscape plugin for activeX components and firefox allows access to activeX components. can i access DOM , webbrowser2 objects in the c++ code or not in netscape and firefox? what abt *inx based system? hope to hear from u guys..... cheers vikram vikram sareen Sign In·View Thread·PermaLink 1.00/5 (2 votes) Debug Informatoion corrupt Adeel688 22:22 21 Jun '06   Whenever I add CWebpage.h and CWebpage.cpp in my project, it generates this error... uuid.lib(cguid_i.obj) : fatal error LNK1103: debugging information corrupt; recompile module what could be the reason for this error? can you tell me how to resolve it? When i remove these files from the project the error goes away. Sign In·View Thread·PermaLink 1.60/5 (3 votes) Reverse task, how to call C++ function from JavaScript? M A V 15:42 21 Jun '06   Hello, Eugene I've read your article "JavaScript call from C++" on CodeProject. It is great and very helpful! But what if I need to solve a reverse task: I have an application with CHtmlView. In my MFC application I have the function "void SizeWindow(int windth, int height)". Now, is there any way I can call it from the JavaScript in HTML page ? Regards, MAV Sign In·View Thread·PermaLink 2.20/5 (5 votes) Re: Reverse task, how to call C++ function from JavaScript? jamesmhall 5:05 30 Mar '07   There are two ways to go the opposite direction. The first is to use new ActiveXObject("App.Class");, where App.Class is the VersionIndependentProgID in the CLSID definition in the registry. NOTE: this will create a *new* instance of your class and you will need to communicate back to the BHO or container class. More ideally, when you have a containing object, such as an explorer bar, you can use window.external.methodName(args); to communicate directly with the parent container. You will need to add the method definition to the IDispatch interface definition for your object. Sign In·View Thread·PermaLink 2.00/5 (1 vote) Re: Reverse task, how to call C++ function from JavaScript? www.add-your-page.com 5:26 8 Oct '08   Hi MAV, I have exactly the same question you had 2 years ago. Did you find a solution to it? My JavaScript: <script language="Javascript"> function TestAlert() { alert("Hello Moto"); // works } function CallToCpp() { // here I'd like to call a function I wrote in C++ MyCppFunction(); // error 'object expected // so how can I link the function to my JavaScript? } </script> I hope anyone can help. Martin Sign In·View Thread·PermaLink 1.00/5 (1 vote) Re: Reverse task, how to call C++ function from JavaScript? M A V 5:58 8 Oct '08   Hello, Martin! Yes, I have solved a problem, it was not trivial. The main idea that you have to substitute COleControlSite for your web browser control and there you can redirect the calls to IDispatch interface. The javascript code will then look like window.external.MyCppFunction(param1,param2); I can give you source code If you contact me by e-mail: mav_stuff@bk.ru Regards, MAV Sign In·View Thread·PermaLink How to get the result www.add-your-page.com 11:07 16 May '06   Nice code, but how can I get the javascript result into a CComBSTR variable rather than a IE popup window? Is this possible Martin Sign In·View Thread·PermaLink 2.50/5 (4 votes) BUG, then calling JavaScript MicroCell 23:06 13 Apr '06   Hello. I was try this function (CallJScript) to call Java function in some HTML document, runing on the different Microsoft Internet Explorer window. This is an simple onchange handler of SELECT tag: <select name="cmb_ReportTraffic_Commission" id="cmb_ReportTraffic_Commission" language="javascript" style="WIDTH: 247px" önchange="cmb_ReportTraffic_Commission_onchange();"> my code: CWebPage wp; CComQIPtr spqiDisp = m_spDoc; wp.SetDocument(spqiDisp); wp.CallJScript(_T("cmb_ReportTraffic_Commission_onchange")); The function do not fall, but the handler was still uncalled. Please help ))) Sign In·View Thread·PermaLink 2.00/5 (1 vote) HOWTO: Return value from C++ function to JavaScript Syed Khasim 5:20 28 Mar '06   I have the following code snippet. CTestApp::ReturnPointer() { ITestPointer *test; HRESULT hr = CoCreateInstance(...,.,(void**)&test); if (SUCCEEDED(hr)) return test; else return NULL; } How can i return the test pointer value to javascript so that i can use it there. Im trying a lot but i cann't .. Please provide me some info on t hat. Please any one tell me, whether it can be done or not. Thanks in advance. syed Syed -- modified at 10:22 Tuesday 28th March, 2006 Sign In·View Thread·PermaLink 2.40/5 (5 votes) Memory leak while dealing parameters. Kim Moung Soo 21:29 9 Mar '06   Source code,WebPage.cpp, in this article has memory leak problem showing below. It uses bstr.CopyTo() to pass BSTR string to argument. In the CComBSTR::CopyTo() function it allocates BSTR string using SysAllocStringByteLen() and copy it to the dispparams.rgvarg[i].bstrVal. , therefore calling SysFreeString() is required before deleting dispparams.rgvarg. for( int i = 0; i < arraySize; i++) { CComBSTR bstr = paramArray.GetAt(arraySize - 1 - i); // back reading bstr.CopyTo(&dispparams.rgvarg[i].bstrVal); } .. hr = spScript->Invoke(dispid,IID_NULL,0, DISPATCH_METHOD,&dispparams,&vaResult,&excepInfo,&nArgErr); /////////////////// bug fix memory leak code start /////////////// for( int j = 0; j < arraySize; j++) ::SysFreeString(dispparams.rgvarg[j].bstrVal); /////////////////// bug fix memory leak code end /////////////// delete [] dispparams.rgvarg; Best regards, -- modified at 2:41 Friday 10th March, 2006 Sign In·View Thread·PermaLink 5.00/5 (1 vote) Re: Memory leak while dealing parameters. M A V 15:44 21 Jun '06   Hello Maybe you could help me.... But what if I need to solve a reverse task: I have an application with CHtmlView. In my MFC application I have the function "void SizeWindow(int windth, int height)". Now, is there any way I can call it from the JavaScript in HTML page ? Regards, MAV Sign In·View Thread·PermaLink 1.00/5 (1 vote) Re: Memory leak while dealing parameters. Pille_0 4:27 22 Sep '06   Thank you very much for this useful bug fix Sign In·View Thread·PermaLink Re: Memory leak while dealing parameters. Amit2203 8:10 1 Jul '07   Still there is memory leak in this funciotn. I can no understand yet where it is come from, but this appear. Anybody found additional memory leak When i comment row: hr = spScript->Invoke(dispid,IID_NULL,0, DISPATCH_METHOD,&dispparams,&vaResult,&excepInfo,&nArgErr); then memory leak disappear Any idea? Sign In·View Thread·PermaLink Getting the url of an object Craig D. 10:37 27 Jul '05   First nice job!! I have one question. After I call my javascript, it loads an image that is embedded on the main document. I know that if I right click and choose properties that I can get full url of the image, but programmtically how can I get the url of that image??? Sign In·View Thread·PermaLink 1.25/5 (4 votes) How to change the UserAgent of embeded browser akhilesh.kumar 8:20 13 Jul '05   Hi, Thanks fo such a usefull example, I have an embeded browser in my application, IS there any way to change the User-Agent of IE browse from my c++ application. This way when scrip in the browser read the User-Agent of browser, it can find out which application has loaded tehis browser. Even appending string to user Agent should be fine. Thanks AK Sign In·View Thread·PermaLink 2.70/5 (6 votes) Re: How to change the UserAgent of embeded browser yu_cg 8:48 4 Sep '07   the API function UrlMkGetSessionOption may help you Everything is possible. Sign In·View Thread·PermaLink access to the HTML elements Jomateix 5:01 15 Mar '05   i'm a beguiner and i'm trying to use javascrtipts that call activex as it were c++ functions but while trying to create a progrma I fall at the first step: what library or control i must import to run : "CComPtr spDisp = CHtmlView::GetHtmlDocument(); m_webPage.SetDocument(spDisp);" thanks if anyone reads aond answer this little question Sign In·View Thread·PermaLink 1.00/5 (1 vote) memory overflow spring 20:30 24 Jan '05   first of all, it's a good ariticle, but after I read the source, I find a memory overflow bug, it's in the "void CJSCallView::OnDocumentComplete(LPCTSTR strURL)" after get the htmldocument, it should call release() method, resut should be: void CJSCallView::OnDocumentComplete(LPCTSTR strURL) { LPDISPATCH pDisp = GetHtmlDocument(); GetDocument()->OnDocumentComplete(strURL,pDisp); pDisp->Release(); } Sign In·View Thread·PermaLink 3.00/5 (2 votes)

Last Visit: 14:18 9 Jul '09     Last Update: 14:18 9 Jul '09 123 Next »