function _inherits(subClass, superClass) {
  if (typeof superClass !== 'function' && superClass !== null) {
    throw new TypeError('Super expression must either be null or a function, not ' + typeof superClass)
  }
  subClass.prototype = Object.create(superClass && superClass.prototype, {
    constructor: {
      value: subClass,
      enumerable: false,
      writable: true,
      configurable: true
    }
  })
  // inherit `Class` static properties
  if (superClass)
    Object.setPrototypeOf ? Object.setPrototypeOf(subClass, superClass) : (subClass.__proto__ = superClass)
}