How can I implement a user notification service using rxjs within Angular?

Question

How can I implement a user notification service using rxjs within Angular?

As a newcomer to reactive programming, I am exploring ways to create an Angular service that can present notifications to the user. Check out what I have accomplished so far:

https://stackblitz.com/edit/angular-rxjs-notifications?file=app%2Fapp.component.html

The main challenge in my implementation lies in figuring out how to queue notifications in a reactive manner. My goal is for the notification div to display when the first notification is pushed, and disappear only when "Clear" is clicked unless more notifications have been added since. This way, clearing would reveal the next notification, continuing until all notifications are cleared. Subsequently, once a new notification is received, the div should reappear.

In my setup, I opted for a Subject instead of a ReplaySubject because I do not want users to see notifications sent while they were loading the next screen. However, I realized that if there is routing within my app.component.html, this behavior may still occur. Perhaps I need to clear the notification queue upon navigation?

Your insights are greatly appreciated!

angular typescript rxjs

Answer 1

Answer №1

Here is an example showcasing the structure of a service:

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import { Subject } from 'rxjs/Subject';
import { merge } from 'rxjs/observable/merge';
import { map, scan } from 'rxjs/operators';

enum ActionType {
  insert = 'insert',
  remove = 'remove'
}

interface Action {
  type: ActionType;
}

interface InsertAction extends Action {
  payload: string;
}

interface RemoveAction extends Action { }

@Injectable()
export class NotificationService {
  messages$: Observable<string[]>;

  private insertSource = new Subject<string>();
  private removeSource = new Subject<void>();

  constructor() {
    const insert$ = this.insertSource.asObservable()
      .pipe(map((payload) => ({ type: ActionType.insert, payload })));

    const remove$ = this.removeSource.asObservable()
      .pipe(map((payload) => ({ type: ActionType.remove })));

    this.messages$ = merge(insert$, remove$)
      .pipe(
      scan((acc: any, { payload, type }) => {
        if (type === ActionType.remove) {
          acc = acc.slice(0, -1);
        }
        if (type === ActionType.insert) {
          acc = [...acc, payload]
        }
        return acc;
      }, [])
      );
  }

  insertMessage(msg: string) {
    this.insertSource.next(msg)
  }

  removeMessage() {
    this.removeSource.next()
  }
}

Check out the live demo here

We utilize two streams, remove$ and insert$, merging them together before reducing to a singular array through the scan operator.

For instance, a sequence like

insert(hello) -> insert(world) -> remove -> insert(kitty)

would be condensed down to [hello, kitty].

Answer 2

Here is an example showcasing the structure of a service:

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import { Subject } from 'rxjs/Subject';
import { merge } from 'rxjs/observable/merge';
import { map, scan } from 'rxjs/operators';

enum ActionType {
  insert = 'insert',
  remove = 'remove'
}

interface Action {
  type: ActionType;
}

interface InsertAction extends Action {
  payload: string;
}

interface RemoveAction extends Action { }

@Injectable()
export class NotificationService {
  messages$: Observable<string[]>;

  private insertSource = new Subject<string>();
  private removeSource = new Subject<void>();

  constructor() {
    const insert$ = this.insertSource.asObservable()
      .pipe(map((payload) => ({ type: ActionType.insert, payload })));

    const remove$ = this.removeSource.asObservable()
      .pipe(map((payload) => ({ type: ActionType.remove })));

    this.messages$ = merge(insert$, remove$)
      .pipe(
      scan((acc: any, { payload, type }) => {
        if (type === ActionType.remove) {
          acc = acc.slice(0, -1);
        }
        if (type === ActionType.insert) {
          acc = [...acc, payload]
        }
        return acc;
      }, [])
      );
  }

  insertMessage(msg: string) {
    this.insertSource.next(msg)
  }

  removeMessage() {
    this.removeSource.next()
  }
}

Check out the live demo here

We utilize two streams, remove$ and insert$, merging them together before reducing to a singular array through the scan operator.

For instance, a sequence like

insert(hello) -> insert(world) -> remove -> insert(kitty)

would be condensed down to [hello, kitty].

How can I implement a user notification service using rxjs within Angular?

Answer №1

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