Elegant.

Singleton is a javascript object. so, with
Singleton.__instance = this;

we are creating a property __instance on the Singleton object and setting its value to this.

The if condition checks if the Singleton object has __instance property on it and returns that if its present, so, basically using the same "this" object everytime.

What I don't get is calling 'Singleton' from within 'Singleton'. Obviously this is allowed so we have some kind of closure and that's why __instance keeps the instance value like a ststic.