Requirements for prototype chain in JS

prototype-chain.js

'use strict';

function Animal (voice) {
  this.voice = voice || 'Grunt'
}

Animal.prototype.speak = function () {
  display(this.voice)
}

function Cat (name, color) {
  Animal.call(this, 'Meow') //1
  this.name = name;
  this.color = color;
}

Cat.prototype = Object.create(Animal.prototype); //2
Cat.prototype.constructor = Cat; // 3
//When we creating the prototype chain, we need lines 1, 2 and 3
var fluffy = new Cat('Fluffy', 'Black');
var muffin = new Cat('Muffin', 'White');

//fluffy.speak();

display(fluffy.__proto__.__proto__)

display(Animal.prototype)