Issue with Typescript: For in loop not identifying object properties

Currently, I am utilizing a loop with for in to iterate through a list of Meeting objects named allMeetings. Inside this loop, I am populating another list called allEvents, where non-Meeting objects will be stored. However, when attempting to access the properties of the Meeting object within the loop, they are not being recognized. I am seeking guidance on how to address or work around this issue.

Details about My Meeting model:

export class Meeting {
    id: UUID;
    date: Date;
    description: string;
}

Concerning the TypeScript File:
The loop is implemented within the makeEvents() method.

...
import { Meeting } from '../models/meeting.model';
import { MeetingsService } from '../services/meetings.service';
...
export class SomeComponent implements OnInit {
    allEvents: SpikesEvent[] = undefined;
    allMeetings: Meeting[] = undefined;

   constructor(private _meetingsService: MeetingsService) { }

    ngOnInit() {
        this.loadMeetings();
        this.makeEvents();
    }

    loadMeetings(): void {
        this._meetingsService.getAllMeetings().subscribe(
            (allMeetings: Meeting[]) => {
                this.allMeetings = allMeetings;
            }
        );
    }

    makeEvents(): void {
        for (let meeting in this.allMeetings) {
            this.allEvents.push({
                start: startOfDay(meeting.date),
                title: meeting.description,
                color: colors.yellowsunflower,
                type: "meeting",
                id: meeting.id,
            });
        }
    }
}

Issues Faced: The properties like date, description, and id of a meeting object are not being recognized.

EDIT 1: Included the constructor in the TypeScript File.
EDIT 2: Just to clarify, I retrieve my data from rethinkDB so there's no JSON file involved. Nonetheless, here's a log entry to confirm that the Meeting object indeed contains data:

date: "Fri Feb 20 1993 00:00:00 GMT+00:00", description: "meeting about dummy data", id: "088c0baf-3c02-48b2-a072-65905fb0c0a7"

Answer №1

It's interesting how the oversight of using a for...in loop to iterate over objects has been overlooked by many. This approach can lead to TypeScript not recognizing the properties properly, as seen in your code snippet.

If you prefer using for-in loops, consider adjusting your implementation like so:

for (let meeting in this.allMeetings) {
    this.allEvents.push({
        start: startOfDay(this.allMeetings[meeting].date),
        //...
    });
}

Alternatively, utilizing the forEach method might offer a more streamlined solution.

While the issue of asynchronous code mentioned in another response is important for runtime execution, it does not directly address the specific problem at hand in your query.

Answer №2

Update your code with the following changes:

ngOnInit() {
    this.fetchAppointments();
}

fetchAppointments(): void {
    this._appointmentsService.getAllAppointments().subscribe(
        (allAppointments: Appointment[]) => {
            this.allAppointments = allAppointments;
            // Ensure to trigger this function only after receiving data in this.allMeetings
            this.generateEvents();
        }
    );
}

Answer №3

To effectively manipulate the data inside the callback, it is important to follow the suggestions provided. For further insights on this issue, you can refer to the following question: How do I return the response from an Observable/http/async call in angular2?

Additionally, instead of using the key as the object, consider using the forEach method. Start by invoking the loadMeetings function and then calling makeEvents within the callback:

ngOnInit() {
    this.loadMeetings();
}

loadMeetings(): void {
   this._meetingsService.getAllMeetings()
     .subscribe((allMeetings: Meeting[]) => {
         this.allMeetings = allMeetings;
            this.makeEvents();
        });
}

The implementation of the makeEvents function would resemble the following code snippet:

makeEvents(): void {
  this.allMeetings.forEach((x:Meeting) => {
     this.allEvents.push({
       start: startOfDay(x.date),
       title: x.description,
       color: colors.yellowsunflower,
       type: "meeting",
       id: x.id,
     })
  })
}

By following these steps, the functionality should align with your requirements. Feel free to check out the demo for a practical example.

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