I'd like to build a wrapper class, that does something before and after each emitted value of an Observable.
Here's what I came up with:
class Wrapper<T> {
wrapped$: Observable<T>;
_dataSubject = new Subject<T>();
data$ = this._dataSubject.pipe(
tap(_ => console.log("BEFORE"),
//
// map( ??? )
//
);
constructor(wrapped$: Observable<T>) {
this.wrapped$ = wrapped$.pipe(
tap(_ => console.log("AFTER")
);
}
}
let subject = new Subject<string>();
let wrapper = new Wrapper(subject);
wrapper.data$.subscribe(val => console.log(val));
subject.next("foo")
The console output should be:
BEFORE
foo
AFTER
I can't figure out how to connect the $wrapped
Observable with the _dataSubject
.
But maybe I'm completely wrong and it needs a different approach.
What about something like this
import {Observable} from 'rxjs';
export class DoBeforeAfter<T> {
wrapped$: Observable<T>;
constructor(wrapped$: Observable<T>, doFunction: (data: any) => void) {
this.wrapped$ = Observable.of(null)
.do(_ => console.log("BEFORE"))
.switchMap(_ => wrapped$)
.do(doFunction)
.do(_ => console.log('AFTER'));
}
}
to be consumed like this
const source = Observable.of('NOW');
const beforeAfter = new DoBeforeAfter(source, data => console.log(data));
beforeAfter.wrapped$.subscribe(
null,
error => console.error(error),
() => console.log('DONE')
)
It looks a bit cumbersome, but maybe it can help