var call = require('../internals/function-call');
var hasOwn = require('../internals/has-own-property');
var isPrototypeOf = require('../internals/object-is-prototype-of');
var regExpFlags = require('../internals/regexp-flags');

var RegExpPrototype = RegExp.prototype;

module.exports = function (R) {
  var flags = R.flags;
  return flags === undefined && !('flags' in RegExpPrototype) && !hasOwn(R, 'flags') && isPrototypeOf(RegExpPrototype, R)
    ? call(regExpFlags, R) : flags;
};