Check internet connection in web using Angular 4

We don’t need any libraries for this however public onlineOffline: boolean = navigator.onLine; will do the trick but this is just a one time check. We need to treat this value as an observable so whenever the online status change we are updated. For this rxjs will help.

Import these

import { Observable, Observer, fromEvent, merge } from 'rxjs';
import { map } from 'rxjs/operators';

Add this method

  createOnline$() {
    return merge<boolean>(
      fromEvent(window, 'offline').pipe(map(() => false)),
      fromEvent(window, 'online').pipe(map(() => true)),
      new Observable((sub: Observer<boolean>) => {
        sub.next(navigator.onLine);
        sub.complete();
      }));
  }

Subscribe to this event from your constructur or ngOnInit

this.createOnline$().subscribe(isOnline => console.log(isOnline));

Note: Im using Angular 8.1 and rxjs 6.5.2