Angular: Communication using Subject in Services

alert.service.ts

import { Injectable } from '@angular/core';
import { Router, NavigationStart } from '@angular/router';
import { Observable } from 'rxjs';
import { Subject } from 'rxjs/Subject';

import { Alert, AlertType } from '../models/alert';

@Injectable()
export class AlertService {
	private subject = new Subject<Alert>();
	private keepAfterRouteChange = false;

	constructor(private router: Router) {
		router.events.subscribe(event => {
			if (event instanceof NavigationStart) {
				if (this.keepAfterRouteChange) {
					this.keepAfterRouteChange = false;
				} else {
					this.clear();
				}
			}
		});
	}

	getAlert(): Observable<any> {
		return this.subject.asObservable();
	}

	success(message: string, keepAfterRouteChange = false) {
		this.alert(AlertType.Success, message, keepAfterRouteChange);
	}

	error(message: string, keepAfterRouteChange = false) {
		this.alert(AlertType.Error, message, keepAfterRouteChange);
	}

	info(message: string, keepAfterRouteChange = false) {
		this.alert(AlertType.Info, message, keepAfterRouteChange);
	}

	warn(message: string, keepAfterRouteChange = false) {
		this.alert(AlertType.Warning, message, keepAfterRouteChange);
	}

	alert(type: AlertType, message: string, keepAfterRouteChange = false) {
		this.keepAfterRouteChange = keepAfterRouteChange;
		this.subject.next(<Alert>{ type: type, message: message });
	}

	clear() {
		this.subject.next();
	}
}

launcher.component.ts

...

this.alertService.success('Alert message);

...

subscriber.component.ts

import { Component, OnInit } from '@angular/core';
import { Alert, AlertType } from '../models/alert';
import { AlertService } from '../services/alert.service';

@Component({
	selector: 'alert',
	templateUrl: 'alert.component.html'
})
export class AlertComponent {
	alerts: Alert[] = [];

	constructor(private alertService: AlertService) {}

	ngOnInit() {
		this.alertService.getAlert().subscribe((alert: Alert) => {
			if (!alert) {
				this.alerts = [];
				return;
			}
			this.alerts.push(alert);
		});
	}

	removeAlert(alert: Alert) {
		this.alerts = this.alerts.filter(x => x !== alert);
	}
}