code: protected Object doTopCall(Callable callable,
                                 Context cx, Scriptable scope,
                                 Scriptable thisObj, Object[] args)
      {
          Object result = callable.call(cx, scope, thisObj, args);
          return result instanceof ConsString ? result.toString() : result;
      }
docs: Execute top call to script or function.
  When the runtime is about to execute a script or function that will
  create the first stack frame with scriptable code, it calls this method
  to perform the real call. In this way execution of any script
  happens inside this function.