__proto__ VS. prototype in JavaScript

javascript prototype javascript-objects prototypal-inheritance
0x90 picture 0x90 · Mar 31, 2012 · Viewed 194.7k times · Source

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?

enter image description here

The figure was taken from dmitrysoshnikov.com.

Answer

Mark Kahn picture Mark Kahn · Mar 31, 2012

__proto__ is the actual object that is used in the lookup chain to resolve methods, etc. prototype is the object that is used to build __proto__ when you create an object with new:

( new Foo ).__proto__ === Foo.prototype;
( new Foo ).prototype === undefined;

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