__proto__ VS. prototype in JavaScript

Question

This figure again shows that every object has a prototype. Constructor function Foo also has its own __proto__ which is Function.prototype, a

Answer 1

To put it simply:

> var a = 1
undefined
> a.__proto__
[Number: 0]
> Number.prototype
[Number: 0]
> Number.prototype === a.__proto__
true

This allows you to attach properties to X.prototype AFTER objects of type X has been instantiated, and they will still get access to those new properties through the __proto__ reference which the Javascript-engine uses to walk up the prototype chain.