Firebase Realtime Database: Observing a Value

const database = firebase.database();
const dbRefVal = database.ref().child('app');

dbRefVal.on('value', snap => {
	console.log('Current version:', snap.val());
});

app can be both a primitive and an object
listener is fired when the value is altered in any way (like added, changed or removed)
when initializing application, existing values are printed though they had existed before the application was run