redux-observable how to keep passing the payload - redux

Question

How can I continue to pass the payload to the rest of my operators?
For example:
login = (action$: ActionsObservable) => {
return action$.ofType(SessionActions.LOGIN_USER)
.mergeMap(({payload}) => {
return this.http.post(`${BASE_URL}/auth/login`, payload)
.map(result => ({
type: SessionActions.LOGIN_USER_SUCCESS,
payload: result.json().meta
}))
.catch(error => Observable.of({
type: SessionActions.LOGIN_USER_ERROR
}));
});
}
How can I pass the payload and the result to the map operator?

Answer 1

The value for payload is available inside the .map because the function is defined with payload in scope. You can use payload within that function with the way it is currently written:
.map(result => ({
type: SessionActions.LOGIN_USER_SUCCESS,
payload: {
one: result.json().meta,
two: payload /* this is in parent scope from mergeMap */
}
}))
However, if you want to make it more explicit, one way is to use zip to combine observables:
login = (action$: ActionsObservable) => {
return action$.ofType(SessionActions.LOGIN_USER)
.mergeMap(({payload}) => {
return Rx.Observable.zip(
Rx.Observable.of(payload),
this.http.post(`${BASE_URL}/auth/login`, payload),
(payload, result) => { payload, result }
)
.map({ payload, result} => ({
type: SessionActions.LOGIN_USER_SUCCESS,
payload: result.json().meta
}))
.catch(error => Observable.of({
type: SessionActions.LOGIN_USER_ERROR
}));
});
}
Zip lets you combine several observables and provide a selector function to form the resulting object. Depending on your intentions, combineLatest may suit your needs for similar problems, when you want the latest value of each source whenever any source emits.