How can I convert a JavaScript array() to an ATL/COM array?

Question

How can I convert a JavaScript array() to an ATL/COM array without using VBArray?

What I want to convert is a new Array() to a SAFEARRAY.

Answer 1

With IActiveScript you can instantiate a JavaScript engine in C++ and use it to:

• Make IDispatch* pointers for JavaScript functions
• Make VARIANT variables containing JavaScript objects
• Pass JavaScript objects to JavaScript functions in C++

Using this technique, we shall do the following:

1. Declare a JavaScript function, e.g. function (arr) { return arr.length; }
2. Declare a JavaScript array, e.g. [2, 3, 5, 7, 11]
3. Call the JavaScript function with the JavaScript array as input

To make this work, you must create an IActiveScriptSite. The following is a C++ console application that demonstrates this concept:

// C++ headers for ATL and Active Script Hosting.
#include 
#include 
#include 

// A minimal implementation of IActiveScriptSite.
class ATL_NO_VTABLE CScriptSite :
    public CComObjectRootEx,
    public IActiveScriptSite,
    public IActiveScriptSiteWindow
{
public:
BEGIN_COM_MAP(CScriptSite)
    COM_INTERFACE_ENTRY(IActiveScriptSite)
    COM_INTERFACE_ENTRY(IActiveScriptSiteWindow)
END_COM_MAP()
    DECLARE_PROTECT_FINAL_CONSTRUCT()
    HRESULT FinalConstruct()
    {
        return S_OK;
    }
    void FinalRelease()
    {
    }
public:
    // IActiveScriptSite
    STDMETHOD(GetLCID)(LCID* plcid)
    {
        *plcid = 0;
        return S_OK;
    }
    STDMETHOD(GetItemInfo)(
        LPCOLESTR pstrName,
        DWORD dwReturnMask,
        IUnknown** ppiunkItem,
        ITypeInfo** ppti)
    {
        return TYPE_E_ELEMENTNOTFOUND;
    }
    STDMETHOD(GetDocVersionString)(BSTR* pbstrVersion)
    {
        *pbstrVersion = ::SysAllocString(L"1.0");
        return S_OK;
    }
    STDMETHOD(OnScriptTerminate)(
        const VARIANT* pvarResult,
        const EXCEPINFO* pexcepinfo)
    {
        return S_OK;
    }
    STDMETHOD(OnStateChange)(SCRIPTSTATE ssScriptState)
    {
        return S_OK;
    }
    STDMETHOD(OnScriptError)(IActiveScriptError* pIActiveScriptError)
    {
        return S_OK;
    }
    STDMETHOD(OnEnterScript)(void)
    {
        return S_OK;
    }
    STDMETHOD(OnLeaveScript)(void)
    {
        return S_OK;
    }
    // IActiveScriptSiteWindow
    STDMETHOD(GetWindow)(HWND* phWnd)
    {
        *phWnd = NULL;
        return S_OK;
    }
    STDMETHOD(EnableModeless)(BOOL fEnable)
    {
        return S_OK;
    }
};

// ATL in a Console app.
CComModule _Module;
BEGIN_OBJECT_MAP(ObjectMap)
END_OBJECT_MAP()

// Main body
int _tmain(int argc, _TCHAR* argv[])
{
    HRESULT hr = S_OK;
    hr = _Module.Init(ObjectMap, NULL, NULL);

    // Instantiate JavaScript engine.
    hr = CoInitializeEx(NULL, COINIT_MULTITHREADED);
    CComObject* pScriptSite = NULL;
    hr = CComObject::CreateInstance(&pScriptSite);
    pScriptSite->AddRef();
    CComPtr spIActiveScript;
    hr = spIActiveScript.CoCreateInstance(OLESTR("JScript"));
    hr = spIActiveScript->SetScriptSite(pScriptSite);
    CComPtr spIActiveScriptParse;
    hr = spIActiveScript->QueryInterface(IID_IActiveScriptParse, (void **) &spIActiveScriptParse);
    hr = spIActiveScriptParse->InitNew();
    hr = spIActiveScript->SetScriptState(SCRIPTSTATE_CONNECTED);

    // Evaluate an anonymous JavaScript function.
    CComVariant vSomeFunc;
    EXCEPINFO ei = { };
    hr = spIActiveScriptParse->ParseScriptText(
        OLESTR("(function () { return function (arr) { return arr.length; }; } )();"),  // pstrCode
        NULL,                       // pstrItemName
        NULL,                       // punkContent
        NULL,                       // pstrDelimiter
        0,                          // dwSourceContextCookie
        0,                          // ulStartingLineNumber
        SCRIPTTEXT_ISEXPRESSION,    // dwFlags
        &vSomeFunc,                 // pvarResult
        &ei                         // pexcepinfo
        );

    // Make a JavaScript array object.
    CComVariant vObject;
    hr = spIActiveScriptParse->ParseScriptText(
        OLESTR("[2,3,5,7,11]"), // pstrCode
        NULL,                       // pstrItemName
        NULL,                       // punkContent
        NULL,                       // pstrDelimiter
        0,                          // dwSourceContextCookie
        0,                          // ulStartingLineNumber
        SCRIPTTEXT_ISEXPRESSION,    // dwFlags
        &vObject,                   // pvarResult
        &ei                         // pexcepinfo
        );

    // Call the anonymous JavaScript function (gives answer of 5).
    CComVariant vResult;
    DISPPARAMS dispParams = { &vObject, 0, 1, 0 };
    hr = V_DISPATCH(&vSomeFunc)->Invoke(
        DISPID_VALUE,
        IID_NULL,
        0,
        DISPATCH_METHOD,
        &dispParams,
        &vResult,
        &ei,
        NULL);

    // Release variables.
    hr = vSomeFunc.Clear();
    hr = vObject.Clear();
    hr = vResult.Clear();

    // Release JavaScript engine.
    spIActiveScriptParse = NULL;
    spIActiveScript = NULL;
    pScriptSite->Release();
    pScriptSite = NULL;
    ::CoUninitialize();
    return 0;
}

To answer the original posters question, we then need to create another JavaScript function to extract elements from the array, say, function (arr,idx) { return arr[idx]; }. Now we have enough functions to walk JavaScript arrays in C++.