It works just fine for me.

Qt Code: 
  1. #include <QtGui>
  2. #include <QtQml>
  3.  
  4. int main(int argc, char **argv) {
  5.   QGuiApplication app(argc, argv);
  6.   QQmlEngine e;
  7.   QQmlComponent c(&e, "test.qml");
  8.   QObject *o = c.create();
  9.   QVariantMap m;
  10.   m["i"] = 10;
  11.   m["name"] = "someName";
  12.   QVariant v = m;
  13.   QVariant ret;
  14.   QMetaObject::invokeMethod(o, "testFunc", Q_RETURN_ARG(QVariant, ret), Q_ARG(QVariant, v));
  15. //  return app.exec();
  16.   return 0;
  17. }
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javascript Code: 
  1. import QtQml 2.0
  2.  
  3. QtObject {
  4.   function testFunc(v) { console.log("v.name = ", v.name); }
  5. }
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