Singleton, return to javascript basics

Simple example of singleton

var MySingleton = (function MySingleton() {
 return {
   // YOUR PUBLIC CODE
   myFunction: function() {},
   myVariable: 2020
 };
})();

MySingleton.myVariable; // Outputs: 2020
MySingleton.myFunction(); // Outputs: void

Combine reactive code and singleton with Rxjs

var MySingleton = (function MySingleton(rxjs) {
 var user$ = new rxjs.BehaviorSubject(null);
 return {
   user$
 };
})(rxjs);

MySingleton.user$.subscribe(function(user) { });

Simple ;)