Executing a Function in a Service from a Component in Angular/TypeScript and Receiving a Return Value

Question

Executing a Function in a Service from a Component in Angular/TypeScript and Receiving a Return Value

I need guidance on how to effectively utilize the "getUserDocInfo()" function from a separate service within my component. How can I call this function and then leverage the data it returns for further operations?

Component Example

 getToken(){
    this.userService.getUserDocInfo();
    // Once the data is returned, I want to extract and use certain values
  }

Service Implementation

getUserDocInfo() {
    this.getUserInfo().then(() => {
      this.userDoc = this.afs.doc(`users/${this.userID}`);
      this.user = this.userDoc.snapshotChanges();
      this.user.subscribe(value => {
        const data = value.payload.data();
      });
    })
  }

 async getUserInfo() {
    const user = await this.authService.isLoggedIn()
    if (user) {
      this.userID = user.uid;
    } else {
      // Handle alternative scenario
    }
  }

If you have any tips or best practices to share regarding this scenario, please feel free to offer your suggestions.

angular typescript google-cloud-firestore angularfire5

Answer 1

Answer №1

If you're looking to accomplish this, one approach is to set up a callback function that can be passed as a parameter in the method. Here's an example:

getUserDocInfo(callback) {
    this.getUserInfo().then(() => {
      this.userDoc = this.afs.doc(`users/${this.userID}`);
      this.user = this.userDoc.snapshotChanges();
      this.user.subscribe(callback);
    })
  }

getToken(){
    this.userService.getUserDocInfo((value) => {
        console.log(value.payload.data());
    });
  }

Another option is to return an Observable and then subscribe to it within your component context for more customized handling.

import { Observable } from 'rxjs/Observable/';
import 'rxjs/add/observable/fromPromise';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/mergeMap';

@Injectable()
export class AlertService {

  //constructor and properties...

  getUserDocInfo(): Observable<any> {
    Observable.fromPromise(this.getUserInfo()).mergeMap(() => {
      this.userDoc = this.afs.doc(`users/${this.userID}`);
      this.user = this.userDoc.snapshotChanges();
      return this.user.map(user => user);
    });
  }
}

@Component(...)
export class MyComponent implements OnDestroy {

  subscriptions: Array<Subscription> = new Array;

  //constructor

  getToken(){
    const sub = this.userService.getUserDocInfo().subscribe((value) => {
        console.log(value.payload.data());
    });
    this.subscriptions.push(sub);
  }

  ngOnDestroy() {
    this.subscriptions.forEach(sub => sub.unsubscribe());
  }
}

Answer 2

If you're looking to accomplish this, one approach is to set up a callback function that can be passed as a parameter in the method. Here's an example:

getUserDocInfo(callback) {
    this.getUserInfo().then(() => {
      this.userDoc = this.afs.doc(`users/${this.userID}`);
      this.user = this.userDoc.snapshotChanges();
      this.user.subscribe(callback);
    })
  }

getToken(){
    this.userService.getUserDocInfo((value) => {
        console.log(value.payload.data());
    });
  }

Another option is to return an Observable and then subscribe to it within your component context for more customized handling.

import { Observable } from 'rxjs/Observable/';
import 'rxjs/add/observable/fromPromise';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/mergeMap';

@Injectable()
export class AlertService {

  //constructor and properties...

  getUserDocInfo(): Observable<any> {
    Observable.fromPromise(this.getUserInfo()).mergeMap(() => {
      this.userDoc = this.afs.doc(`users/${this.userID}`);
      this.user = this.userDoc.snapshotChanges();
      return this.user.map(user => user);
    });
  }
}

@Component(...)
export class MyComponent implements OnDestroy {

  subscriptions: Array<Subscription> = new Array;

  //constructor

  getToken(){
    const sub = this.userService.getUserDocInfo().subscribe((value) => {
        console.log(value.payload.data());
    });
    this.subscriptions.push(sub);
  }

  ngOnDestroy() {
    this.subscriptions.forEach(sub => sub.unsubscribe());
  }
}

Executing a Function in a Service from a Component in Angular/TypeScript and Receiving a Return Value

Answer №1

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