save(form) {
   if (form.valid) {
     if (this.postId) {
       const post = form.value
       post.id = this.postId
       this.posts.patch(post)
     } elseĀ {
       this.posts.add(form.value)
     }
     this.router.parent.navigate(['PostList'])
   }
 }
  constructor(private routeParams: RouteParams, private router: Router, public posts: Posts) {
    this.postId = routeParams.get('id')
    this.post$ = !!this.postId ? posts.load(this.postId) : new Subject().startWith({
      title: 'nouveau post'
    })

    this.post$.subscribe(data => {
      this.title = data.title
    })
  }
 constructor(public posts: Posts) {
   posts.loadAll()
 }