code: private boolean validTypeOfVarExpression(Node expr) {
   // The expression must have two children:
      // - The typeOfVar keyword
      // - A string
      if (!checkParameterCount(expr, Keywords.TYPEOFVAR)) {
        return false;
      }
      if (!getCallArgument(expr, 0).isString()) {
        warnInvalid("name", expr);
        warnInvalidInside(Keywords.TYPEOFVAR.name, expr);
        return false;
      }
      return true;
    }
docs: A typeOfVar expression must be of the form typeOfVar('name')