I'm new to observables in angular. I have a problem wanting to return a value inside a subscribe method. I have
the following method (getFirebaseData(idForm:string):observable <any[]>
):
getTotalQuestions(idForm:string){
let totalQuestions:number;
this.getFirebaseData(idForm+"/Metadatos")
.subscribe(items =>
{
items.map(item => {
totalQuestions=item.Total;
console.log(totalQuestions);
});
}
);
console.log(totalQuestions);
return totalQuestions;
}
the firts console.log(totalQuestions)
print 4 but the second console.log(totalQuestions)
print undefined.
I understand that subscribe is an asynchronous operation and that for that reason the second console.log(totalQuestions)
("In order to write the code") print undefined, but I can not find the way to return the variable after the subscribe method has been completed. Now, if I change the subscribe to map:
getTotalQuestions(idForm:string){
let totalQuestions:number;
this.getFirebaseData(idForm+"/Metadatos")
.subscribe(items =>
{
items.map(item => {
totalQuestions=item.Total;
console.log(totalQuestions);
});
}
);
console.log(totalQuestions);
return totalQuestions;
}
the firts console.log(totalQuestions)
does not print anything and the second console.log(totalQuestions)
print undefined. It's something that I do not understand because it happens.
I hope you can help me clarify the concept that I do not understand. Thanks!
You can't directly return totalQuestions like that, you need to use a subject to achieve that.
getTotalQuestions(idForm:string): Observable<string> {
let totalQuestions:number;
var subject = new Subject<string>();
this.getFirebaseData(idForm+"/Metadatos")
.subscribe(items => {
items.map(item => {
totalQuestions=item.Total;
console.log(totalQuestions);
subject.next(totalQuestions);
});
}
);
return subject.asObservable();
}
Usage: getTotalQuestion(idForm).subscribe((r)=>console.log(r))