Assuming that < 600px means mobile to you, you can use this observable and subscribe to it:
First we need the current window size. So we create an observable which only emits a single value: the current window size.
initial$ = Observable.of(window.innerWidth > 599 ? false : true);
Then we need to create another observable, so that we know when the window size was changed. For this we can use the "fromEvent" operator. To learn more about rxjs`s operators please visit: rxjs
resize$ = Observable.fromEvent(window, 'resize').map((event: any) => {
return event.target.innerWidth > 599 ? false : true;
});
Merg these two streams to receive our observable:
mobile$ = Observable.merge(this.resize$, this.initial$).distinctUntilChanged();
Now you can subscribe to it like this:
mobile$.subscribe((event) => { console.log(event); });
Remember to unsubscribe :)