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JavaScript call from C++

, 7 Jul 2011 CPOL
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A class for easy implementation of JavaScript calls from C++ code.

Sample Image

Introduction

Sometimes when you 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 easily 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 control for a JavaScript object inside of an HTML page is possible by using the traditional COM approach. This article describes the class CWebPage which allows to do it and a technique to call a JavaScript function from C++ code.

How to do

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

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

The rest of the things will be done by the CWebPage class. Here is an example of a JavaScript call without parameters:

m_webPage.CallJScript("Welcome");

An example of a JavaScript call with two parameters will looks like:

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 above mentioned technique can be split into the following steps:

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

Here is an example of getting an IDispatch pointer to the JavaScript objects:

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

And here is the final function to call JavaScript:

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 a function in the tree in the left window. After this, press the "!" button on the menu bar.

History

  • July 07, 2011: Updated download files.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Eugene Khodakovsky
Software Developer (Senior)
United States United States
No Biography provided

Comments and Discussions

 
GeneralRe: calling java from c++ PinmemberMember 470826628-May-10 6:13 
QuestionHi can anybody help me Pinmembersrinileo23-Sep-08 16:46 
GeneralIHTMLDocument without window PinmemberMuran26-Aug-08 1:52 
GeneralRe: IHTMLDocument without window PinmemberMuran26-Aug-08 3:27 
GeneralRe: IHTMLDocument without window PinmemberDabara26-Aug-09 5:25 
QuestionHow to call external JavaScript ? Pinmembernaren_code21-Jun-07 5:48 
AnswerRe: How to call external JavaScript ? Pinmemberbumbumtrack2-Jul-07 20:52 
Generalsupport for firefox Pinmembervikram19798-Aug-06 5:04 
GeneralDebug Informatoion corrupt PinmemberAdeel68821-Jun-06 22:22 
QuestionReverse task, how to call C++ function from JavaScript? PinmemberM A V21-Jun-06 15:42 
AnswerRe: Reverse task, how to call C++ function from JavaScript? Pinmemberjamesmhall30-Mar-07 5:05 
AnswerRe: Reverse task, how to call C++ function from JavaScript? Pinmemberwww.add-your-page.com8-Oct-08 5:26 
GeneralRe: Reverse task, how to call C++ function from JavaScript? PinmemberM A V8-Oct-08 5:58 
GeneralRe: Reverse task, how to call C++ function from JavaScript? Pinmembermarkhatsell5-Oct-10 6:55 
AnswerRe: Reverse task, how to call C++ function from JavaScript? PinmemberM A V5-Oct-10 9:13 
GeneralRe: Reverse task, how to call C++ function from JavaScript? Pinmembermarkhatsell6-Oct-10 10:53 
AnswerRe: Reverse task, how to call C++ function from JavaScript? PinmemberSergey Alexander Gynech9-Jul-11 13:58 
QuestionHow to get the result Pinmemberwww.add-your-page.com16-May-06 11:07 
GeneralBUG, then calling JavaScript PinmemberMicroCell13-Apr-06 23:06 
GeneralHOWTO: Return value from C++ function to JavaScript PinmemberSyed Khasim28-Mar-06 5:20 
GeneralMemory leak while dealing parameters. PinmemberKim Moung Soo9-Mar-06 21:29 
GeneralRe: Memory leak while dealing parameters. PinmemberM A V21-Jun-06 15:44 
AnswerRe: Memory leak while dealing parameters. PinmemberPille_022-Sep-06 4:27 
GeneralRe: Memory leak while dealing parameters. PinmemberAmit22031-Jul-07 8:10 
GeneralRe: Memory leak while dealing parameters. Pinmemberthucnh4-May-10 21:55 

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