Observables from Array typescript

Question

I want to create an observable from array, but I am getting error (A tuple type element list cannot be empty) every time. I have tried a lot, but still it's not working.

 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);
 }

what error do you get?

Kevin Kloet
– Kevin Kloet

2017-09-22 07:02:55 +00:00
Commented Sep 22, 2017 at 7:02 — Kevin Kloet
– Kevin Kloet, Commented Sep 22, 2017 at 7:02
Try Observable.create(donationsHistory)

Rajesh Dixit
– Rajesh Dixit

2017-09-22 07:03:14 +00:00
Commented Sep 22, 2017 at 7:03 — Rajesh Dixit
– Rajesh Dixit, Commented Sep 22, 2017 at 7:03
It's not working, still same error.

Abhay
– Abhay

2017-09-22 07:05:07 +00:00
Commented Sep 22, 2017 at 7:05 — Abhay
– Abhay, Commented Sep 22, 2017 at 7:05
@kevin, A tuple type element list cannot be empty

Abhay
– Abhay

2017-09-22 07:07:39 +00:00
Commented Sep 22, 2017 at 7:07 — Abhay
– Abhay, Commented Sep 22, 2017 at 7:07

cartant · Accepted Answer · 2017-09-22 07:21:54Z

3

The problem is in the function's signature:

listdonationsHistory(): Observable<[]>

Specifically, it's the return type. That is where the empty tuple is.

To declare the return type as an observable that emits an arbitrary array, you could use:

listdonationsHistory(): Observable<any[]>

However, in the implementation you are calling Observable.from and the returned observable will emit the array elements separately - in which case the return type should be Observable<any>.

If you want an observable that will emit array itself, you should use Observable.of instead of Observable.from.

edited Sep 22, 2017 at 7:21

answered Sep 22, 2017 at 7:11

cartant

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4 Comments

Rajesh Dixit Over a year ago

Which is more preferred, any[] or Array<any>?

cartant Over a year ago

They are the same and different people have differing opinions. I prefer the former, wherever possible.

Abhay Over a year ago

@cartant, I have tried it also, but it is also not working. And neither I am getting a specific error in this case. I only get runtime error for this.

cartant Over a year ago

I've updated the answer - it's not clear whether you want the returned observable to emit the array itself, or the array's elements individually. The answer now explains the difference between calling Observable.from and Observable.of.

kimy82 · Accepted Answer · 2017-09-22 07:48:01Z

1

I can see a problem there. The return type is not an array it is an object. If you want the observable to be an array use Observable.of instead of Observable.from

Try that:

    interface Somereturn {
      id: number;
    }

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

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

answered Sep 22, 2017 at 7:48

kimy82

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1 Comment

Abhay Over a year ago

I have tried that Observable.of also, but didn't get the solution. Bt Yes there is one thing I am not using Interface.

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