How to subscribe to class method that returns a rxjs observable?

Question

I have a class method that uses BehaviorSubject and fromFetch from rxjs and returns an observable. I'm trying to subscribe to method outside of class.

I can console.log the method I get AnonymousSubject {_isScalar: false, observers: Array(0), closed: false, isStopped: false, hasError: false, …}

export class Client {
  constructor(opts) {
    ...
  }
  request(operation) {
    const option$ = new BehaviorSubject(null)
    const body = JSON.stringify({
      query: operation.query,
      variables: operation.variables
    })
    option$.next(body)

    return option$.pipe(
      switchMap(body => {
        return fromFetch(url, {
          method: 'POST',
          body,
          headers: {
            'Content-Type': 'application/json',
            ...fetchOpts.headers
          },
          ...fetchOpts
        }).pipe(
          switchMap(response => {
            if (response.ok) {
              // OK return data
              return response.json()
            } else {
              // Server is returning a status requiring the client to try something else.
              return of({
                error: true,
                message: `Error ${response.status}`
              })
            }
          }),
          catchError(err => {
            // Network or other error, handle appropriately
            console.error(err)
            return of({ error: true, message: err.message })
          })
        )
      })
    )
  }
}

I'm want to call method and subscribe to it like so

let client = new Client({...})

function handleRequest(operations) {
  let data = client.request(operations)
  data.subscribe(...)
}

When I add .subscribe to data it throws error: Uncaught TypeError: You provided an invalid object where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.

I hope it is just a typo while posting this code. Still, want to confirm - Did you try const option$ = new BehaviorSubject<any>(null); BehaviorSubject must be of a type with an initial value. — user2216584

user2216584 user2216584 · Accepted Answer · 2019-06-12T00:17:11

Problem is that you are returning simple response.json() You should return an observable like of(response.json()) from switchMap's if (response.ok) block - See the code below -

export class Client {
  constructor(opts) {
    ...
  }
  request(operation) {
    const option$ = new BehaviorSubject(null)
    const body = JSON.stringify({
      query: operation.query,
      variables: operation.variables
    })
    option$.next(body)

    return option$.pipe(
      switchMap(body => {
        return fromFetch(url, {
          method: 'POST',
          body,
          headers: {
            'Content-Type': 'application/json',
            ...fetchOpts.headers
          },
          ...fetchOpts
        }).pipe(
          switchMap(response => {
            if (response.ok) {
              // OK return data
              return of(response.json())
            } else {
              // Server is returning a status requiring the client to try something else.
              return of({
                error: true,
                message: `Error ${response.status}`
              })
            }
          }),
          catchError(err => {
            // Network or other error, handle appropriately
            console.error(err)
            return of({ error: true, message: err.message })
          })
        )
      })
    )
  }
}

How to subscribe to class method that returns a rxjs observable?

1 Answers