How to subscribe and unsubscribe the window load event in Rxjs

I know every web programmers are aware of adding window.addeventlistener to ensure some codes are executing once when loading the web page. You can remove the listener by removing using removeEventListener to make avoid the memory leak.

You can do the same thing in a RxJs fashion using take(1). So you no need to unsubscribe it explicitly to avoid the memory leak.
var onWindowLoad=Observable.fromEvent(window,'load');

var onLoadSubscription=onWindowLoad.take(1).forEach(function(event){