How Do I Handle Asynchronous Responses from Observables in Angular?

How do I return the response from an Observable/http/async call in angular?

Problem:

Retrieving data from a server in Angular using an Observable can result in an undefined initial value if attempted immediately.

Service:

@Injectable()
export class EventService {
  ...
  getEventList(): Observable<any> {
    ...
    return this.http.get(...).map(...).catch(...);
  }
}

Component:

export class EventComponent {
  myEvents: any;
  ngOnInit() {
    this.es.getEventList().subscribe((response) => {
      this.myEvents = response;
    });
    console.log(this.myEvents); // Initially undefined
  }
}

Reason:

The HTTP request is asynchronous, meaning the console.log(this.myEvents) line executes before the response arrives.

Solution:

Handle the response only after it arrives by using the subscribe callback.

ngOnInit() {
  this.es.getEventList().subscribe((response) => {
    this.myEvents = response;
    console.log(this.myEvents); // Not undefined
  });
}

Considerations:

• Perform all operations within the subscribe callback when the data arrives.
• Recognize that async operations prevent interface freezing while waiting for responses.
• This approach is similar to the then callback in Promise-based asynchronous programming.

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