prototype.__proto__ と util.inherits() の違い

test1.js

function Animal() {}
function Ferret() {}
Ferret.prototype.eat = true;
Ferret.prototype.__proto__ = Animal.prototype;
Ferret.prototype.bark = false;
var ferret = new Ferret();
console.log(ferret.eat, ferret.bark);

test2.js

function Animal() {}
function Ferret() {}
Ferret.prototype.eat = true;
require('util').inherits(Ferret, Animal);
Ferret.prototype.bark = false;
var ferret = new Ferret();
console.log(ferret.eat, ferret.bark);

結果：

> node ./test1.js
true false
> node ./test2.js
undefined false