docs: public static boolean instanceOf(Object a, Object b, Context cx)
      {
          // Check RHS is an object
          if (! (b instanceof Scriptable)) {
              throw typeError0("msg.instanceof.not.object");
          }
  
          // for primitive values on LHS, return false
          if (! (a instanceof Scriptable))
              return false;
  
          return ((Scriptable)b).hasInstance((Scriptable)a);
      }