smaple-angular-es6.js

// Ordinarily, you would import this from another module...
class ObservableService {
  constructor() {
    this.callbacks = [];
  }
  subscribe(cb) {
    this.callbacks.push(cb)
  }
  notify() {
    this.callbacks.forEach(cb => {
      cb();
    })
  }
}

class BookingService extends ObservableService {
  constructor(AEMConfig) {
    super();
    // Use an injected property. 
    this.aemConfig = AEMConfig;
  }

  update() {
    // Do something
  }

  static bookingFactory(AEMConfig) {
    return new BookingService(AEMConfig);
  }
}
BookingService.bookingFactory.$inject = ['AEMConfig'];
angular.module('booking').factory('Booking', BookingService.bookingFactory);