Error in Angular 7: Trying to assign a 'void' type to a 'ObservableInput<{}>' type

I can't seem to understand why I am encountering this error

  fetchFromURL(url: string): any {
    return this.apiService.get(url).pipe(map(data => data));
  }

  fetchNextPage(): Observable<any> {
    const url = 'url';
    this.fetchFromURL(url).pipe(
      expand(data => {
        console.log(data);
      })
    );
  }

The error I encountered is at the line containing expand(data => ... . I would like to use expand() so that I can recursively call the next API.

Type 'void' is not assignable to type 'ObservableInput<{}>'

Any suggestions would be greatly appreciated. Thank you

javascriptangulartypescriptrxjsngrx

Answer №1

To ensure correct data handling, it is essential to verify the data type of the 'data' variable and ensure it is returned properly within your method.

fetchNextPageData(): Observable<any> {
    const url = 'url';
    this.fetchDataFromURL(url).pipe(
      expand(data => {
        console.log(data);
        return data;
      })
    );
  }

Answer №2

enhance(output => {
  display.log(output);
})

The implementation you provided lacks a return value, resulting in a void. To rectify this, ensure you return an observable.

Answer №3

The reason for the issue is due to incorrect usage of the expand() operator. According to the documentation, the expand() operator should return an Observable, but in your case, it is not returning anything.

Even if you are returning the "data" variable, the error will persist because of this specific rule.

I recommend checking out this documentation

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