I implemented an method which returns an Observable. Inside this method I am using http.post to send a request to the backend. After receiving the response, which is a JSON object, I want to store this in an Observable variable and return that variable. But somehow I didn't manage to solve that problem. In .subscribe the res variable is not stored in the postResponse variable, but I can see in the "local" console.log that the res variable has the correct value. The global console.log is empty. Furthermore I get the error:
"TS2322: Type 'ArqResponse' is not assignable to type 'Observable'" error for the return.
My code looks like this:
postARQRequest(request): Observable<ArqResponse>{
let postResponse = new ArqResponse;
const result = this.http.post<ArqResponse>(this.arqUrl, request)
.subscribe((res: ArqResponse) => { postResponse = res; console.log('shadow: ' + res)});
console.log('global: ' + JSON.stringify(postResponse));
return postResponse;
}
My questions are:
.subscribe
seems to be wrong since I get: this.arqService.postARQRequest(...).subscribe is not a function error
I'm guessing this is what you want:
postARQRequest(request): Observable<ArqResponse>{
return this.http.post<ArqResponse>(this.arqUrl, request);
}
There's no need to subscribe to anything here. Given that this.http.post
returns the type you want, just return that.
If you really want to store the response in a local variable, there are some ways to do that:
Use a promise instead, for getting the result. Make it observable using of
later on:
async postARQRequest(request): Observable<ArqResponse>{
let postResponse = new ArqResponse;
postResponse = await this.http.post<ArqResponse>(this.arqUrl, request).toPromise();
return of(postResponse);
}
Use the tap
operator to react to the response, but not mutate it
postARQRequest(request): Observable<ArqResponse>{
return this.http.post<ArqResponse>(this.arqUrl, request).pipe(
tap((res) => ...) // do stuff with res here, but it won't be mutated
);
}
Use the map
operator to map the response to something else
postARQRequest(request): Observable<ArqResponse>{
return this.http.post<ArqResponse>(this.arqUrl, request).pipe(
map((res) => ...) // do stuff with res here, but it *will map to whatever you return from this handler*
);
}
I think this may help you
postARQRequest(): Observable<ArqResponse[]> {
return this.http.post(this.arqUrl, request)
.map(this.extractData()) <== passing result of function
.catch(this.handleError()); <== passing result of function
}
handle response and error here
private extractData(res: Response) {
let body = res.json();
return body.data || { };
}
private handleError (error: any) {
let errMsg = error.message || 'Server error';
console.error(errMsg);
return Observable.throw(errMsg);
}
YThe method http.post
already return an Observable
, so you can directly do like that:
postARQRequest(request): Observable<ArqResponse>{
return this.http.post<ArqResponse>(this.arqUrl, request);
}
and then subscribe to it: this.arqService.postARQRequest(...).subscribe()
If you want to transform an object to an Observable, you can use of
from Rxjs6 :
import { of } from 'rxjs';
// ...
// create an Observable from a value:
of(someObject);
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