rxjs observable angular 2 on localstorage change

Question

I am trying to create an observable that returns values when changes to a localStorage variable happens. My subscriber is not getting the new values upon changes to localStorage (or for that matter an in memory variable).

navbar.component.js

    import { Component, OnInit } from '@angular/core';
    import { UserService } from '../services/user.service';

    /**
     * This class represents the navigation bar component.
     */
    @Component({
      moduleId: module.id,
      selector: 'sd-navbar',
      templateUrl: 'navbar.component.html',
      styleUrls: ['navbar.component.css'],
      providers: [UserService]
    })

    export class NavbarComponent implements OnInit {
      loggedIn: boolean;
      constructor(private us: UserService) { }

      ngOnInit() {
        this.us.isLoggedIn().subscribe(loggedIn => {
          this.loggedIn = loggedIn;
        });
      }
    }

auth.component.ts

    import { Component, OnInit } from '@angular/core';
    import { ActivatedRoute } from '@angular/router';
    import { UserService } from '../shared/services/user.service';

    /**
     * This class represents the lazy loaded AuthComponent.
     */
    @Component({
      moduleId: module.id,
      selector: 'sd-auth',
      templateUrl: 'auth.component.html',
      styleUrls: ['auth.component.css'],
      providers: [UserService]
    })
    export class AuthComponent implements OnInit {
      authParams = {
        provider: '',
        params: {}
      };

      constructor(private route: ActivatedRoute, private us: UserService) { }
      ngOnInit() {
        this.route.params.forEach((param) => {
          this.authParams.provider = param.authprovider;
        });

        this.route.queryParams.forEach((queryParams) => {
          this.authParams.params = queryParams;
        });

        this.us.logIn("google", JSON.stringify(this.authParams));

        console.log(JSON.parse(localStorage.getItem('authParams')));

      }
    }

user.service.ts

    // user.service.ts
    import { Injectable } from '@angular/core';
    import { Observable } from 'rxjs/Observable';
    import { Subscriber } from 'rxjs/Subscriber';

    @Injectable()
    export class UserService {
      private loggedIn = false;
      private logger = new Observable<boolean>((observer: Subscriber<boolean>) => {
        observer.next(this.loggedIn);
      });
      constructor() {
        if (localStorage.getItem('authParams')) {
          this.loggedIn = !!JSON.parse(localStorage.getItem('authParams')).params.id_token;
        } else {
          this.loggedIn = false;
        }
      }

      logIn(provider: string, providerResponse: string) {
        localStorage.setItem('authParams', providerResponse);
        this.loggedIn = true;
      }

      isLoggedIn(): Observable<boolean> {
        return this.logger;
      }

      logOut() {
        localStorage.removeItem('authParams');
        this.loggedIn = false;
      }
    }

Flow looks like

Step 1- Navbar subscribes to UserService (Gets the default value of loggedIn=false) Step 2 - AuthComponent updates UserService (sets loggedIn = true)

My subscription in Navbar is not getting updated. What am I missing here. Do I need to put something in the logIn method of UserService like event emitter?

Answer 1

What you want is a Subject. Check out the docs here.

For a quick example, something like this:

export class UserService {
  ...
  private logger = new Subject<boolean>();
  ...

  isLoggedIn(): Observable<boolean> {
    return this.logger.asObservable();
  }

  logIn(provider: string, providerResponse: string) {
    localStorage.setItem('authParams', providerResponse);
    this.loggedIn = true;
    this.logger.next(this.loggedIn);
  }

  logOut() {
    localStorage.removeItem('authParams');
    this.loggedIn = false;
    this.logger.next(this.loggedIn);
  }
...

Answer 2

I wrote a StorageService to support Observable localStorage and sessionStorage. It supports both in one service.

StorageService

import { BehaviorSubject, Observable } from 'rxjs';

/**
 * Storage service
 * used for persist application data in observable key value pair
 */
export class StorageService {

    private storage: Storage;
    private subjects: Map<string, BehaviorSubject<any>>;

    /**
     * Constructor with service injection
     * @param storage 
     */
    constructor(storage: Storage) {
        this.storage = storage;
        this.subjects = new Map<string, BehaviorSubject<any>>();
    }

    /**
    * watch data of given key
    * @param key 
    * @param defaultValue 
    */
    watch(key: string): Observable<any> {
        if (!this.subjects.has(key)) {
            this.subjects.set(key, new BehaviorSubject<any>(null));
        }
        var item = this.storage.getItem(key);
        if (item === "undefined") {
            item = undefined;
        } else {
            item = JSON.parse(item);
        }
        this.subjects.get(key).next(item);
        return this.subjects.get(key).asObservable();
    }

    /**
     * get data of given key
     * @param key 
     */
    get(key: string): any {
        var item = this.storage.getItem(key);
        if (item === "undefined") {
            item = undefined;
        } else {
            item = JSON.parse(item);
        }
        return item;
    }

    /**
     * set value on given key
     * @param key 
     * @param value 
     */
    set(key: string, value: any) {
        this.storage.setItem(key, JSON.stringify(value));
        if (!this.subjects.has(key)) {
            this.subjects.set(key, new BehaviorSubject<any>(value));
        } else {
            this.subjects.get(key).next(value);
        }
    }

    /**
    * remove given key
    * @param key 
    */
    remove(key: string) {
        if (this.subjects.has(key)) {
            this.subjects.get(key).complete();
            this.subjects.delete(key);
        }
        this.storage.removeItem(key);
    }

    /**
     * clear all available keys
     */
    clear() {
        this.subjects.clear();
        this.storage.clear();
    }
}

LocalStorageService

import { Injectable, Inject } from '@angular/core';
import { StorageService } from './storage.service';

/**
 * Local storage service
 * used for persist application data in observable key value pair
 */
@Injectable()
export class LocalStorageService extends StorageService {

    /**
     * Constructor with service injection
     * @param window 
     */
    constructor(@Inject('WINDOW') private window: any) {
        super(window.localStorage);
    }
}

SessionStorageService

import { Injectable, Inject } from '@angular/core';
import { StorageService } from './storage.service';

/**
 * Session storage service
 * used for persist application data in observable key value pair
 */
@Injectable()
export class SessionStorageService extends StorageService {

    /**
     * Constructor with service injection
     * @param window 
     */
    constructor(@Inject('WINDOW') private window: any) {
        super(window.sessionStorage);
    }
}

This is how you can use the service:

import { LocalStorageService } from './local-storage.service';

export class TestClass implements OnInit, OnDestroy {

    constructor(
        private localStorage: LocalStorageService,
    ) { }

    ngOnInit() {
        // get current value
        this.localStorage.get('foo');

        // set new value
        this.localStorage.set('foo', 'bar');

        // watch value changes
        this.localStorage.watch('foo').pipe(takeUntil(this.unsubscribe)).subscribe(foo => console.log('foo changed', foo));
    }

    ngOnDestroy() {
        this.unsubscribe.next();
        this.unsubscribe.complete();
    }
}

(I'm really new to TypeScript with a couple of month experience. Any improvements or recommendations are welcome :-) )

Answer 3

An alternative is to observe the storage event

fromEvent(window, 'storage').subscribe((storageEvent) => {
  //do what you need to do with your storageEvent
})

This means you dont need to wrap the native API in any service layer.

Answer 4

To be more precise, use BehaviourSubject from import { BehaviorSubject } from 'rxjs/BehaviorSubject';

For ex:

    @Injectable()
    export class UserService {

      public username = new BehaviorSubject<string>('');
      public preferredLanguage = new BehaviorSubject<string>('');
      public preferredTimezone = new BehaviorSubject<string>('');

      constructor(
        private router: Router,
        private jwtTokenService: JwtTokenService
      ) {
        let token: string = localStorage.getItem('token'); // handled for page hard refresh event
        if (token != null) {
          this.decode(token);
        }
      }

      private decode(token: string) {
        let jwt: any = this.jwtTokenService.decodeToken(token);
        this.username.next(jwt['sub']);
        this.preferredLanguage.next(jwt['preferredLanguage']);
        this.preferredTimezone.next(jwt['preferredTimezone']);
      }

      public setToken(token: any) {
        localStorage.setItem('auth_token', token);
        this.decode(token);
      }

    }

and to learn difference between BehaviorSubject and Observable: BehaviorSubject vs Observable?