import { Injectable } from ‘@angular/core‘;import {RealtimeService} from "../shared";import {FirebaseListObservable} from "angularfire2";@Injectable()export class CourseService {  courses$: FirebaseListObservable<any>;  public lastCourse: any;  constructor(private rt: RealtimeService) {    this.courses$ = rt.getCourseObs();    this.getLastCourse();  }  addCourse(course){    return this.courses$.push(course)      .then(        success => success.key,        err => console.error("err", err)      );  }  removeCourse(course){    return this.courses$.remove(course)      .then(        () => "OK",        err => console.error("err", err)      );  }  updateCourse(course, updates){    return this.courses$.update(course, updates)      .then(        () => "OK",        err => console.error("err", err)      );  }  getLastCourse(){    this.courses$      .subscribe(        courses => {          this.lastCourse = courses[courses.length - 1]        }      )  }}