Observing Array behaviors in TypeScript

Question

Observing Array behaviors in TypeScript

Struggling to generate an observable from an array due to the recurring error message (A tuple type element list cannot be empty). Despite multiple attempts, I'm unable to resolve this issue.

 listDonationsHistory(): Observable<[]> {
     const donationsHistory = [
        {
          id :1,
          type :"Aeri",
          amount: 200,
          frequency: 'monthly',
          date: '17-09-2017',
          account:'ATYTYTYY6778'
        },
        {
          id :2,
          type :"Aeri",
          amount: 200,
          frequency: 'monthly',
          date: '17-09-2017',
          account:'ATYTYTYY6778'
        }
      ];
    return Observable.from(donationsHistory);
 }

javascript typescript rxjs observable

Answer 1

Answer №1

The issue lies within the function's signature:

listdonationsHistory(): Observable<[]>

In particular, it's the type of return value. This is where the empty tuple is present.

If you want to specify the return type as an observable that emits a random array, you could change it to:

listdonationsHistory(): Observable<any[]>

However, since you are using Observable.from in the implementation and the elements in the array are emitted separately, the return type should be Observable<any>.

If you prefer an observable that emits the array itself, consider using Observable.of instead of Observable.from.

Answer 2

The issue lies within the function's signature:

listdonationsHistory(): Observable<[]>

In particular, it's the type of return value. This is where the empty tuple is present.

If you want to specify the return type as an observable that emits a random array, you could change it to:

listdonationsHistory(): Observable<any[]>

However, since you are using Observable.from in the implementation and the elements in the array are emitted separately, the return type should be Observable<any>.

If you prefer an observable that emits the array itself, consider using Observable.of instead of Observable.from.

Answer 3

Answer №2

It seems there is a problem in the code. The return type should be an array instead of an object. To fix this, you can change Observable.from to Observable.of

Here's a revised version:


    interface DonationRecord {
        id: number;
    }

    listDonationsHistory(): Observable<DonationRecord> {
        return Observable.from([{id: 2}, {id: 3}]);
    }

    listDonationsHistory(): Observable<DonationRecord[]> {
        return Observable.of([{id: 2}, {id: 3}]);
    }

Answer 4

It seems there is a problem in the code. The return type should be an array instead of an object. To fix this, you can change Observable.from to Observable.of

Here's a revised version:


    interface DonationRecord {
        id: number;
    }

    listDonationsHistory(): Observable<DonationRecord> {
        return Observable.from([{id: 2}, {id: 3}]);
    }

    listDonationsHistory(): Observable<DonationRecord[]> {
        return Observable.of([{id: 2}, {id: 3}]);
    }

Observing Array behaviors in TypeScript

Answer №1

Answer №2

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