Object is of type 'unknown'

Question

I have simple Rxjs function Observables and Operators to return new Observable.in my code i am using filter and map operators chained inside a pipe sadly, i get error TS2571: Object is of type 'unknown'. inside filter operator data The code is following :

import { filter, map, Observable } from 'rxjs'

@Component({
  selector: 'app-observable-operator',
  templateUrl: './observable-operator.component.html',
  styleUrls: ['./observable-operator.component.css']
})
export class ObservableOperatorComponent{

  title:string='Angular Observable using Observable Operators';

  ob=new Observable((observer:any)=>{
    console.log("Observable Starts");
    observer.next(1)
    observer.next(2)
    observer.next(3)
    observer.next(4)
    observer.next(5)
    observer.complete()
  }).pipe(filter(data=>
    data > 2), //Error inside filter operator (parameter) data:unknown
    map((val)=>{return val as number*2}),

  )

}

I'm most certain that you can simply define `ob=new Observable(...)` and everything else falls into place without `any`s and `unknown`s — Thomas, Dec 20 '21 at 05:06

Spankied · Answer 1 · 2021-12-20T05:18:49.213

3

I believe you need to add typing to the param

filter((data: any) => data > 2)

edited Dec 20 '21 at 05:18

answered Dec 20 '21 at 04:05

Spankied

1,626
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21

yes !! it works Thank you very much – Farukh Shaikh Dec 20 '21 at 04:10
Ayy! Feel free to hit that checkmark button under points to mark this as the answer, and I get lil extra :) – Spankied Dec 20 '21 at 04:12

score 0 · Answer 2 · answered Dec 20 '21 at 09:36

The way to fix this issue is to define the type of the observer right.

The observer parameter in the function passed to the constructor of the Observable is of type Observer<number>, since it notifies numbers. If you do this, Typescript can infer the type of data as number.

In other words the code should be this

ob=new Observable((observer: Observer<number>)=>{
  console.log("Observable Starts");
  observer.next(1)
  observer.next(2)
  observer.next(3)
  observer.next(4)
  observer.next(5)
  observer.complete()
}).pipe(filter(data=>
  data > 2), //Error inside filter operator (parameter) data:unknown
  map((val)=>{return val as number*2}),

)

Object is of type 'unknown'

2 Answers2