This figure again shows that every object has a prototype. Constructor function Foo also has its own
__proto__which is Function.prototype, and which in turn also references via its__proto__property again to the Object.prototype. Thus, repeat, Foo.prototype is just an explicit property of Foo which refers to the prototype of b and c objects.
var b = new Foo(20);
var c = new Foo(30);````
What are the differences between __proto__ and prototype properties?
來源：http://stackoverflow.com/questions/9959727/proto-vs-prototype-in-javascript