const orgsArr = [];
organizations.map(orgid => {
this.afs.collection('users').doc<Organization>(orgid).valueChanges()
.map(x => {
orgsArr.push(x);
}).subscribe();
});
return Observable.of(orgsArr);
orgsArr resturns before subscribe()
You're mixing asynchronous code with synchronous code. Your method calls orgsArr.push from within an observable .map call, which won't have executed by the time you return Observable.of(orgsArr)
You're also mis-using map on organizations.map, as map is meant to return something and constructs an array.
You can re-factor this to use a concat with all the Observable returned from the orgs mapped valueChanges() and then a reduce to convert a stream of values into a single array:
const orgValueObsArray = organizations.map(orgid => {
return this.afs.collection('users').doc<Organization>(orgid).valueChanges();
});
return Observable.concat(...orgValueObsArray)
.reduce((acc, val) => {
acc.push(val);
return acc;
}, []);
Related
export const loginSuccess = createAsyncThunk(
"auth/loginSuccess",
async (user: User) => {
const res = await api
.post(
"/auth/loginSuccess",
{ user },
{
withCredentials: true,
}
)
.then((res: any) => {
setAxiosToken(res.data.token);
saveToken(res.data.token);
return { ...res.data.data, token: res.data.token };
});
return res;
}
);
There are 2 return statements at the end so I am confused about which return value the fulfilled reducer will get. The code is written by someone else that's why I want to understand it.
The second return statement is the one which will return from your function.
The first is actually returning from the then function of the promise that axios returns.
This is made a little bit confusing by using the same name for the res variable in the thunk function, and for the response variable that is passed on the the then function.
But what you will receive back is the object generated in this line of code:
{ ...res.data.data, token: res.data.token }
Where res.data.data is spread into a new object, and res.data.token is assigned to the token property of that object.
I've ran into this issue quite a few times where I want to access action.payload further down the chain. But by then, the argument passed to mergeMap has already changed to something else.
Given my action looks like this:
{
type: BUY_GEMS,
payload: { value: 123, productIdentifier: "ABC123" }
}
And this epic:
function purchaseGems(action$, store) {
return action$
.ofType(BUY_GEMS)
.mergeMap(action => {
const { productIdentifier } = action.payload; // <-------- works because it's the first mergeMap in this sequence
return Observable.fromPromise(
// Some promise call
).catch(error => Observable.of(buyGemsRejected(error)));
})
.mergeMap(action => {
const { value } = action.payload; // <----------- doesn't work because "action" is now just the response of the Promise above.
...
});
}
How would I do this?
This trick is to just place your second mergeMap inside the closure where the action is available. In fact, even if you didn't need access to it I generally recommend this pattern in redux-observable whereby you isolate your Observable chains inside your single top-level merging strategy operator (mergeMap, switchMap, etc) because it makes future refactoring like this easier as well as easier error isolation (if added).
function purchaseGems(action$, store) {
return action$
.ofType(BUY_GEMS)
.mergeMap(action => {
const { productIdentifier } = action.payload;
return Observable.fromPromise(somePromise)
.catch(error => Observable.of(buyGemsRejected(error)))
.mergeMap(response => {
const { value } = action.payload;
// ...
});
});
}
Your example contained Observable.fromPromise() which I assume is just pseudo code, so I followed suit with Observable.fromPromise(somePromise) for more clarity for other readers.
in TypeScript, to resolve the promise, I use the await keyword.
but that keyword is only allowed to exist in the body of async functions, which return Promise<T>.
in that case, the function that calls this async function, will need to resolve the return value: Promise<T>, which means i'll again need the await keyword, and that function will have to be defined as async as well.
What am I missing?
You don't have to await, you can use then on the promise.
Here's the scenario you've described:
async function fn(): Promise<number> {
return new Promise<number>((resolve, reject) => {
setTimeout(resolve.bind(null, 2), 1500);
});
}
async function fn2(num: number) {
return await fn() * num;
}
function fn3(num: number) {
fn2(num).then(num => {
console.log(`returned number: ${num}`);
})
}
fn3(10);
(code in playground)
Which outputs this after 1500 milliseconds:
returned number: 20
Edit
Doing this:
var x = fn2(3).then(num => { return num * 2 });
console.log(x);
Will log something like:
Promise {[[PromiseStatus]]: "pending", [[PromiseValue]]: undefined}
To get the value you need to use then:
x.then(num => console.log(num));
You can not assign the result of an async operation into a variable without using await.
I am trying to call a function located in service class,and if that function returns data,one boolean variable sets true. I have 2 class as bollow:student.ts and service.ts:
// student.ts
public ngOnInit() {
this.config.load().then(() => {
this.service.getRecords().then(
function () { console.log("success getRecord");
this.loading = false; },
function () { console.log("failed getRecord");
this.loading = true; });
});
}
//service.ts
public getRecord(id: number): Promise<T> {
return this.getRecordImpl();
}
private getRecordsImpl(): Promise<T[]> {
let url = this.serviceUrl;
return this.http.get(url, this.getRequestOptionsWithToken())
.toPromise()
.then(res => {
this.records = this.extractData<T[]>(res);
for (var i = 0; i < this.records.length; i++) {
var record = this.records[i];
this.onRecord(record);
}
return this.records;
})
.catch(this.handleError);
}
by the now, records from service returns, but this.service.getRecords(); is undefined. and I can't use
.then
for handling succeed and failure actions.
I know that it is not good idea to make it synchronous. but think that being Asynchronous causes getRecords becomes undefined. What is the solution for handling that. I want it runs sequentially. and if service returns any records , variable initialize to false, otherwise it sets to true.
Many thanks for any help and guide.
I think your aproach is not correct, what is the point to make a promise synchronous ? If you really really want to do this I suggest you to dig in the Synchronous programming with es6 generators but usually the job is done much smother.
From your code I see that you are consuming your Promise by attaching .then() in the service. In this way you should create a new Promise.
private getRecordsImpl(): Promise<T[]> {
let url = this.serviceUrl;
return new Promise((resolve, reject) => {
this.http.get(url, this.getRequestOptionsWithToken())
.toPromise()
.then(res => {
this.records = this.extractData<T[]>(res);
for (var i = 0; i < this.records.length; i++) {
var record = this.records[i];
this.onRecord(record);
}
resolve(this.records);
})
.catch(this.handleError);
})
}
And in your code use:
this.service.getRecords().then(
function (records) { console.log("success getRecord");
this.loading = false; },
function (err) { console.log("failed getRecord");
this.loading = true; });
I'm writing a small utility function that wrap a call to AngularJS http.get with the necessary authentication headers:
get(endpoint: string): Observable {
var headers = new Headers();
this._appendAuthentificationHeaders( headers, this.user.credentials);
return this.http.get(endpoint, { headers: headers })
.map(res => res.json());
}
The point here is that if this.user is null, the method will just crash.
So I have three options:
Return null and check that return value on every call...
Throw an exception
Find a way to also return an RxJS Observable object that will directly trigger the error handler.
I would like to implement the third method, as it would allow me unify this method's behavior: It always returns an observable no matter what happen.
Do you have an idea about how to do that?
Do I have to create a new Observable and kind of merge those two?
What can I do?
If the user is null, you can simply return a raw observable that triggers an error:
if (this.user == null) {
return Observable.create((observer) => {
observer.error('User is null');
});
}
(...)
or leverage the throw operator:
if (this.user == null) {
return Observable.throw('User is null');
}
(...)
This way the second method of the subscribe method will be called:
observable.subscribe(
(data) => {
(...)
},
(err) => {
// Will be called in this case
}
);
I think the cleanest way would be to wrap the whole function body to an observable, as it will turn any accidental error to an observable error. Something like this:
get(endpoint: string): Observable {
return Rx.Observable.defer(() => {
var headers = new Headers();
this._appendAuthentificationHeaders(headers, this.user.credentials);
return Rx.Observable.just(headers);
})
.flatMap(headers => this.http.get(endpoint, { headers: headers }))
.map(res => res.json());
}
However I still do not agree with http.get returning an observable instead of a promise. As these are single valued observables, your function could be a simple async function (sry, js instead of ts):
async get(endpoint) {
var headers = new Headers();
this._appendAuthentificationHeaders(headers, this.user.credentials);
const res = await this.http.get(endpoint, { headers })).toPromise();
return res.json();
}