freezeMethods = (obj) => {
  reduceDescriptors(obj, (descriptor, name) => {
    // skip restricted props in strict mode
    if (isFunction(obj) && ['arguments', 'caller', 'callee'].indexOf(name) !== -1) {
      return false;
    }

    const value = obj[name];

    if (!isFunction(value)) return;

    descriptor.enumerable = false;

    if ('writable' in descriptor) {
      descriptor.writable = false;
      return;
    }

    if (!descriptor.set) {
      descriptor.set = () => {
        throw Error('Can not rewrite read-only method \'' + name + '\'');
      };
    }
  });
}
Makes all methods read-only
@param {Object} obj