Angular 7 ComponentCanDeactivate

component-can-deactivate.ts

import {HostListener} from '@angular/core';
import {Observable} from 'rxjs';

export abstract class ComponentCanDeactivate {

    abstract get saved(): boolean;

    abstract canDeactivate(): Observable<boolean> | Promise<boolean> | boolean

    @HostListener('window:beforeunload', ['$event'])
    unloadNotification($event: any): void {
        if (!this.saved) {
            $event.returnValue = true;
        }
    }
}