How to properly make a subscribe inside another subscribe?

Question

Angular

addPost() {
    this.openDialog().subscribe(formData => {
      if (formData) {
        this.postsService.add(formData).subscribe((res: Post) => {
          this.posts.unshift(res);
        });
      }
    });
  }

Answer 1

don't do that, use flatMap

this
  .openDialog()
  .flatMap(fd=>{
     return !fd?Observable.Empty():this.postsService.add(fd).first();
  })
  .subscribe(post=>{
    this.posts.unshift(post);
  });

Answer 2

maybe like this

async addPost() {
   const formData = await this.openDialog().toPromise();
   if (formData) {
    const res = await this.postsService.add(formData).toPromise();
     this.posts.unshift(res);
   }
  }