wait for asynchronous functions to finish in Angular

Question

So I was working on a new component in Angular and in the ngOninit I have the following asynchronous functions below...

This.getUserProfile needs to be finished before I can call this.getPrivateGroup() and this.getPrivateGroup() needs to be finished before I can call this.loadGroupPosts(). I know I could write these functions inside the callback of the asynchronous requests, but I was wondering if there is a way to keep it in ngOnInit to keep it cleaner?

Anyone has an idea?

ngOnInit() {

    this.getUserProfile();

    // my-workplace depends on a private group and we need to fetch that group and edit
    // the group data before we proceed and get the group post
    if (this.isItMyWorkplace) {
      this.getPrivateGroup();
    }
    this.loadGroupPosts();
  }

getUserProfile() {
    this._userService.getUser()
      .subscribe((res) => {
        this.user = res.user;
        console.log('log user', this.user);
        this.profileImage = res.user['profile_pic'];
        this.profileImage = this.BASE_URL + `/uploads/${this.profileImage}`;
      }, (err) => {
        this.alert.class = 'alert alert-danger';
        if (err.status === 401) {
          this.alert.message = err.error.message;
          setTimeout(() => {
            localStorage.clear();
            this._router.navigate(['']);
          }, 3000);
        } else if (err.status) {
          this.alert.class = err.error.message;
        } else {
          this.alert.message = 'Error! either server is down or no internet connection';
        }
      });
  }



getPrivateGroup() {
    console.log('user check', this.user);
    this.groupService.getPrivateGroup(`${this.user.first_name}${this.user.last_name}`)
      .subscribe((group) => {
          console.log('received response', group)
    })
  }

 // !--LOAD ALL THE GROUP POSTS ON INIT--! //
  loadGroupPosts() {
    this.isLoading$.next(true);

    this.postService.getGroupPosts(this.group_id)
      .subscribe((res) => {
        // console.log('Group posts:', res);
        this.posts = res['posts'];
        console.log('Group posts:', this.posts);
        this.isLoading$.next(false);
        this.show_new_posts_badge = 0;
      }, (err) => {
        swal("Error!", "Error while retrieving the posts " + err, "danger");
      });
  }
  // !--LOAD ALL THE GROUP POSTS ON INIT--! //

Have a look at [this stack overflow answer](https://stackoverflow.com/a/35268597/2435263) — dream88, Dec 17 '18 at 15:08
Possible duplicate of [Chaining RxJS Observables from http data in Angular2 with TypeScript](https://stackoverflow.com/questions/35268482/chaining-rxjs-observables-from-http-data-in-angular2-with-typescript) — dream88, Dec 17 '18 at 15:10

sandrooco · Accepted Answer · 2018-12-17T16:20:42.383

You can use basic promises with async/await.

async ngOnInit() {

    await this.getUserProfile(); // <-- 1. change

    // my-workplace depends on a private group and we need to fetch that group and edit
    // the group data before we proceed and get the group post
    if (this.isItMyWorkplace) {
      this.getPrivateGroup();
    }
    this.loadGroupPosts();
  }

async getUserProfile() {
    this._userService.getUser()
      .subscribe((res) => {
        this.user = res.user;
        console.log('log user', this.user);
        this.profileImage = res.user['profile_pic'];
        this.profileImage = this.BASE_URL + `/uploads/${this.profileImage}`;
        return true; // <-- this
      }, (err) => {
        this.alert.class = 'alert alert-danger';
        if (err.status === 401) {
          this.alert.message = err.error.message;
          setTimeout(() => {
            localStorage.clear();
            this._router.navigate(['']);
          }, 3000);
        } else if (err.status) {
          this.alert.class = err.error.message;
        } else {
          this.alert.message = 'Error! either server is down or no internet connection';
        }
        throw err;
      });

}

Thank you for your response. Is it possible I would have to add async next to ngOninit for it to work? — tilly, Dec 17 '18 at 15:27
Check the edited answer - I think it should also work with a proper async function. Not sure if you know it: by returning something out of async functions we resolve the promise it creates (which is awaited in the `ngOnInit`). — sandrooco, Dec 17 '18 at 16:21

score 5 · Answer 2 · edited Nov 04 '20 at 01:45

5

You could instead leverage RxJS and use a switchMap something like this (syntax NOT checked):

getData(): Observable<string[]> {
  return this._userService.getUser()
    .pipe(
      switchMap(userInfo=> {
         return this.getPrivateGroup();
      }),
      catchError(this.someErrorHandler)
    );
}

edited Nov 04 '20 at 01:45

Leniel Maccaferri

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answered Dec 17 '18 at 17:38

DeborahK

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score 1 · Answer 3 · answered Dec 17 '18 at 15:09

One way to do is, return the Observable instead of subscribing in the getPrivateGroup()

getPrivateGroup() {
    console.log('user check', this.user);
    return this.groupService.getPrivateGroup(`${this.user.first_name}${this.user.last_name}`)

  }

And then, subscribe to the data where you want the chain the this.loadGroupPosts()

     if (this.isItMyWorkplace) {
          this.getPrivateGroup().subscribe(group => {
          this.group = group; //you probably want to assign the group data
          this.loadGroupPosts()});
        }

score 0 · Answer 4 · answered Feb 28 '22 at 15:23

you could also use the 3rd part of your subscribe function when its completed i am not quite sure if this is a clean solution, in my opinion it is.

ngOnInit() {
this.getUserProfile();
}


getUserProfile() {
this._userService.getUser()
    .subscribe((res) => {
        this.user = res.user;
        console.log('log user', this.user);
        this.profileImage = res.user['profile_pic'];
        this.profileImage = this.BASE_URL + `/uploads/${this.profileImage}`;
    }, (err) => {
        this.alert.class = 'alert alert-danger';
        if (err.status === 401) {
            this.alert.message = err.error.message;
            setTimeout(() => {
                localStorage.clear();
                this._router.navigate(['']);
            }, 3000);
        } else if (err.status) {
            this.alert.class = err.error.message;
        } else {
            this.alert.message = 'Error! either server is down or no internet connection';
        }
    }, () => {
        // my-workplace depends on a private group and we need to fetch that group and edit
        // the group data before we proceed and get the group post
        if (this.isItMyWorkplace) {
            this.getPrivateGroup();
        }
    });
}

getPrivateGroup() {
console.log('user check', this.user);
this.groupService.getPrivateGroup(`${this.user.first_name}${this.user.last_name}`)
    .subscribe((group) => {
        console.log('received response', group)
    }, error => {
        console.log(error)
    }, () => {
        this.loadGroupPosts();
    })
}

loadGroupPosts() {
this.isLoading$.next(true);

this.postService.getGroupPosts(this.group_id)
    .subscribe((res) => {
        // console.log('Group posts:', res);
        this.posts = res['posts'];
        console.log('Group posts:', this.posts);
        this.isLoading$.next(false);
        this.show_new_posts_badge = 0;
    }, (err) => {
        swal("Error!", "Error while retrieving the posts " + err, "danger");
    });
}

wait for asynchronous functions to finish in Angular

4 Answers4

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