I'm starting with learning how to use RxJS and I have implemented an epic with a conditional Ajax call like this:
export default (action$, store) =>
action$.ofType(GET_USERS_BY_ID)
.mergeMap((action) => {
const userIdList = action.userIdList;
let observable;
if (userIdList.length > 0) {
observable = ajax.get('api/user', { userIdList });
} else {
observable = Observable.of({
response: {}
});
}
return observable
.mergeMap((payload) => {
doSomething1(payload);
doSomething2(payload);
});
});
Is this the right way to do it, or are there some operators that simplify this?
If you only want to process actions where the userIdList has items in it, then you can filter them before making the ajax call, eg.
export default (action$, store) =>
action$.ofType(GET_USERS_BY_ID)
.filter(action => userIdList.length > 0)
.mergeMap((action) => {
const userIdList = action.userIdList;
return ajax.get('api/user', { userIdList })
.mergeMap((payload) => {
doSomething1(payload);
doSomething2(payload);
});
});
Related
We are using .pipe(takeUntil) in the logincomponent.ts. What I need is, it should get destroyed after successful log in and the user is on the landing page. However, the below snippet is being called even when the user is trying to do other activity and hitting submit on the landing page should load different page but the result of submit button is being overridden and taken back to the landing page.
enter code hereforkJoin({
flag: this.auth
.getEnvironmentSettings('featureEnableQubeScan')
.pipe(take(1)),
prefs: this.auth.preferences.pipe(take(1)),
}).subscribe(
(result: any) => {
this.qubeScanEnabled = result.flag.featureEnableQubeScan;
this.userPrefs = result.prefs;
// check to see if we're authed (but don't keep listening)
this.auth.authed
.pipe(takeUntilComponentDestroyed(this))
.subscribe((payload: IJwtPayload) => {
if (payload) {
this.auth.accountO
.pipe(takeUntilComponentDestroyed(this))
.subscribe((account: IAccount) => {
if (this.returnUrl) {
this.router.navigateByUrl(this.returnUrl);
} else {
this.router.navigate(['dashboard']);
}
}
}
}
}
);
ngOnDestroy() {}
Custom Code:
export function takeUntilComponentDestroyed(component: OnDestroy) {
const componentDestroyed = (comp: OnDestroy) => {
const oldNgOnDestroy = comp.ngOnDestroy;
const destroyed$ = new ReplaySubject<void>(1);
comp.ngOnDestroy = () => {
oldNgOnDestroy.apply(comp);
destroyed$.next(undefined);
destroyed$.complete();
};
return destroyed$;
};
return pipe(
takeUntil(componentDestroyed(component))
);
}
Please let me know what I am doing wrong.
Versions:
rxjs: 6.5.5
Angular:10.0.8
Thanks
I've done a first pass at creating a stream that doesn't nest subscriptions and continues to have the same semantics. The major difference is that I can move takeUntilComponentDestroyed to the end of the stream and lets the unsubscibes filter backup the chain. (It's a bit cleaner and you don't run the same code twice every time through)
It's a matter of taste, but flattening operators are a bit easier to follow for many.
enter code hereforkJoin({
flag: this.auth
.getEnvironmentSettings('featureEnableQubeScan')
.pipe(take(1)),
prefs: this.auth.preferences.pipe(take(1)),
}).pipe(
tap((result: any) => {
this.qubeScanEnabled = result.flag.featureEnableQubeScan;
this.userPrefs = result.prefs;
}),
mergeMap((result: any) => this.auth.authed),
filter((payload: IJwtPayload) => payload != null),
mergeMap((payload: IJwtPayload) => this.auth.accountO),
takeUntilComponentDestroyed(this)
).subscribe((account: IAccount) => {
if (this.returnUrl) {
this.router.navigateByUrl(this.returnUrl);
} else {
this.router.navigate(['dashboard']);
}
});
This function doesn't create another inner stream (destroyed$). This way is a bit more back to the basics so it should be easier to debug if you're not getting the result you want.
export function takeUntilComponentDestroyed<T>(comp: OnDestroy): MonoTypeOperatorFunction<T> {
return input$ => new Observable(observer => {
const sub = input$.subscribe({
next: val => observer.next(val),
complete: () => observer.complete(),
error: err => observer.error(err)
});
const oldNgOnDestroy = comp.ngOnDestroy;
comp.ngOnDestroy = () => {
oldNgOnDestroy.apply(comp);
sub.unsubscribe();
observer.complete();
};
return { unsubscribe: () => sub.unsubscribe() };
});
}
app.js
const mapStateToProps = (state) => {
return {home:state}
}
const mapDispatchToProps = (dispatch) => {
return {
guestLogin: (data)=>{dispatch(guestLogin(data)).then(()=>{
dispatch(initiateTrans(stateProps.home))
})},
};
}
const mergeProps = (stateProps, dispatchProps, ownProps) => {
return Object.assign({}, ownProps, stateProps, dispatchProps,{
initiateTrans: () => dispatchProps.initiateTrans(stateProps.home),
})
}
Action.js
export const guestLogin= (state)=>{
var data={
'email':state.email,
'name':state.name,
'phone_number':state.ph_number,
'phone_code':state.country_code
}
return function(dispatch) {
return dataservice.guestSignup(data).then(res => {
dispatch(afterLoggedGuest(res))
}).catch(error => {
throw(error);
});
}
}
function afterLoggedGuest(result) {
return {type: guestLoginChange, result};
}
export const initiateTrans= (updatedState)=>{
return function(dispatch) {
return dataservice.initiateTransaction(updatedState).then(res => {
console.log("initiateTransaction",res)
}).catch(error => {
throw(error);
});
}
}
Reducer.js
if(action.type === guestLoginChange){
return {
...state,guestData: {
...state.guestData,
Authorization: action.result.authentication ,
auth_token: action.result.auth_token ,
platform: action.result.platform
} ,
}
}
I am having two api requests.. After first api request success i want to update state value then pass that updated state to another api request..
I tried to get the updted props
how to dispatch the initiateTrans with update props
I need to update value at api request success in call back i need to call one more request with updated state value
currently i am not able to get the update props value
I think this is a good use case for thunk (redux-thunk), which is a middleware that allows you to execute multiple dispatches in an action.
You will need to apply the middleware when you configure the initial store (see docs on link above). But then in your actions, you can wrap the code with a dispatch return statement, which gives you access to multiple calls. For example:
export const guestLogin= (state)=>{
return dispatch => {
var data={...} // some data in here
return dataservice.guestSignup(data).then(res => {
dispatch(afterLoggedGuest(res))
}).catch(error => {
throw(error);
// could dispatch here as well...
});
}
}
I am learning to use RXJS. In this scenario, I am chaining a few async requests using rxjs. At the last mergeMap, I'd like to have access to the first mergeMap's params. I have explored the option using Global or withLatest, but neither options seem to be the right fit here.
const arraySrc$ = from(gauges).pipe(
mergeMap(gauge => {
return readCSVFile(gauge.id);
}),
mergeMap((csvStr: any) => readStringToArray(csvStr.data)),
map((array: string[][]) => transposeArray(array)),
mergeMap((array: number[][]) => forkJoin(uploadToDB(array, gauge.id))),
catchError(error => of(`Bad Promise: ${error}`))
);
readCSVFile is an async request which returns an observable to read CSV from a remote server.
readStringToArray is another async request which returns an observable to convert string to Arrays
transposeArray just does the transpose
uploadToDB is async DB request, which needs gague.id from the first mergeMap.
How do I get that? It would be great to take some advice on why the way I am doing it is bad.
For now, I am just passing the ID layer by layer, but it doesn't feel to be correct.
const arraySrc$ = from(gauges).pipe(
mergeMap(gauge => readCSVFile(gauge.id)),
mergeMap(({ data, gaugeId }: any) => readStringToArray(data, gaugeId)),
map(({ data, gaugeId }) => transposeArray(data, gaugeId)),
mergeMap(({ data, gaugeId }) => uploadToDB(data, gaugeId)),
catchError(error => of(`Bad Promise: ${error}`))
);
Why don't you do simply this?
const arraySrc$ = from(gauges).pipe(
mergeMap(gauge => readCSVFile(gauge.id).pipe(
mergeMap((csvStr: any) => readStringToArray(csvStr.data)),
map((array: string[][]) => transposeArray(array)),
mergeMap((array: number[][]) => forkJoin(uploadToDB(array, gauge.id)))
)),
catchError(error => of(`Bad Promise: ${error}`))
);
You can also wrap the inner observable in a function:
uploadCSVFilesFromGaugeID(gaugeID): Observable<void> {
return readCSVFile(gaugeID).pipe(
mergeMap((csvStr: any) => readStringToArray(csvStr.data)),
map((array: string[][]) => transposeArray(array)),
mergeMap((array: number[][]) => forkJoin(uploadToDB(array, gaugeID))
);
}
In order to do this at the end:
const arraySrc$ = from(gauges).pipe(
mergeMap(gauge => uploadCSVFileFromGaugeID(gauge.id)),
catchError(error => of(`Bad Promise: ${error}`))
);
MergeMap requires all observable inputs; else, previous values may be returned.
It is a difficult job to concatenate and display the merging response. But here is a straightforward example I made so you can have a better idea. How do we easily perform sophisticated merging.
async playWithBbservable() {
const observable1 = new Observable((subscriber) => {
subscriber.next(this.test1());
});
const observable2 = new Observable((subscriber) => {
subscriber.next(this.test2());
});
const observable3 = new Observable((subscriber) => {
setTimeout(() => {
subscriber.next(this.test3());
subscriber.complete();
}, 1000);
});
console.log('just before subscribe');
let result = observable1.pipe(
mergeMap((val: any) => {
return observable2.pipe(
mergeMap((val2: any) => {
return observable3.pipe(
map((val3: any) => {
console.log(`${val} ${val2} ${val3}`);
})
);
})
);
})
);
result.subscribe({
next(x) {
console.log('got value ' + x);
},
error(err) {
console.error('something wrong occurred: ' + err);
},
complete() {
console.log('done');
},
});
console.log('just after subscribe');
}
test1() {
return 'ABC';
}
test2() {
return 'PQR';
}
test3() {
return 'ZYX';
}
The following code works. It does an ajax request and then call 2 actions, on at a time:
export const loadThingsEpic = action$ => {
return action$.ofType(LOAD_THINGS)
.mergeMap(({things}) => {
const requestURL = `${AppConfig.serverUrl()}/data/things`;
return ajax.getJSON(requestURL)).map(response => {
return finishLoadingThings(response);
}).map(() => {
return sendNotification('success');
});
})
.catch(e => {
return concat(of(finishLoadingThings({ things: {} })),
of(sendNotification('error')));
});
}}
But this code does not:
export const loadThingsEpic = action$ => {
return action$.ofType(LOAD_THINGS)
.mergeMap(({things}) => {
const requestURL = `${AppConfig.serverUrl()}/data/things`;
return ajax.getJSON(requestURL).switchMap(response => {
return concat(of(finishLoadingThings(response)),
of(sendNotification('success')));
});
})
.catch(e => {
return concat(of(finishLoadingThings({ things: {} })),
of(sendNotification('error')));
});
}
I've replace the map by a switchMap to merge 2 actions together (as seen in many other post). It works in the catch if an exception is thrown. I'm wondering whats wrong with the code. I'm guessing it's because I can't seem to really grasp when to use: map, swicthMap and mergeMap.
sendNotification and finishLoadingthings returns action object:
export function finishLoadingThings(data: any) {
return {
type: FINISH_LOADING_THINGS,
data,
};
}
Thanks!
The code provided as-is appears to work as intended: https://jsbin.com/becapin/edit?js,console I do not receive a "invalid object where stream expected" error when the ajax succeeds or fails.
Are you sure the error is coming from this code?
On a separate note, you might be happy to hear that Observable.of supports an arbitrary number of arguments, each one will be emitted after the other. So instead of this:
.switchMap(response => {
return concat(of(finishLoadingThings(response)),
of(sendNotification('success')));
});
You can just do this:
.switchMap(response => {
return of(
finishLoadingThings(response),
sendNotification('success')
);
});
This would not have caused a bug though, it's just cleaner.
I manage to fix my problem, by doing the switchMap at the same level than the mergeMap. Like this:
export const loadThingsEpic = action$ => {
return action$.ofType(LOAD_THINGS)
.mergeMap(({things}) => {
const requestURL = `${AppConfig.serverUrl()}/data/things`;
return ajax.getJSON(requestURL).switchMap(response => {
return of(response);
});
})
.switchMap((res) => {
return concat(of(finishLoadingThings(res.value)),
of(sendNotification('success')));
})
.catch(e => {
return concat(of(finishLoadingThings({ things: {} })),
of(sendNotification('error')));
});
}
Don't quite get it yet.
I'm trying to detect when all my observables have completed. I have the following Observables:
let observables:any[] = [];
if(valid){
observables.push(new Observable((observer:any) => {
async(()=>{
observer.next();
observer.complete();
})
}))
}
if(confirmed){
observables.push(new Observable((observer:any) => {
async(()=>{
observer.next();
observer.complete();
})
}))
}
Observable.forkJoin(observables).subscribe(
data => {
console.log('all completed');
},
error => {
console.log(error);
}
);
I need to do something whenever all my functions are completed. Forkjoin seems to work when the observables array is not empty. But when the array is empty, it never gets called. How can I solve this?
you are missing the 3rd callback in subscribe. try this:
Rx.Observable.forkJoin([]).subscribe(
val => {
console.log('next');
},
err => {
console.log('err');
},
() => {
console.log('complete')
}
);
forkJoin on empty array completes immediately.
Updated for RxJS 6:
let rep: Observable<any>[] = [];
for (let i = 0; i < areas.length; i++) { // undetermined array length
rep.push(this.httpService.GET('/areas/' + areas[i].name)); // example observable's being pushed to array
}
if (rep !== []) {
forkJoin(rep).subscribe(({
next: value => {
console.log(value)
}
}));
}
Try this:
import { forkJoin, Observable, of } from 'rxjs';
export function forkJoinSafe<T = any>(array: Observable<T>[]): Observable<T[]> {
if (!array.length) {
return of([])
}
return forkJoin<T>(array);
}
You're missing complete callback. You can pass the third argument or pass an observer object instead of 3 arguments to make event checking more readable.
yourObservable.subscribe({
next: value => console.log(value),
error: error => console.log(error),
complete: () => console.log('complete'),
});