JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/dojo/1.10.0/dijit/themes/claro/claro.css">

JavaScript

require(["dojo/_base/declare"], function(declare) {
  var Animal = declare(null, {
    constructor: function() {}
  });
  var Dog = declare(Animal, {
    constructor: function() {
         this.items = [];   
    }
  });

  var dog = new Dog();
  dog.items.push(1);
  dog.items.push(2);

  var dog2 = new Dog();
  dog2.items.push(3);

  alert('dog has in items ' + dog.items.length);
  alert('dog2 has in items ' + dog2.items.length);
});