JSFiddle - React, Tailwind, and code Playground

JavaScript

var animal = 
    {
        "eyes": undefined,
        "feet": undefined,
        "languages": 0,
        "friends": [],
        
        "speak": function ()
        {
            this.language = "English"
            this.languages++;
        },
        
        "addFriend": function (friend)
        {
            this.friends.push(friend)
        }
    };

var duck = 
    {
        "feet": 2
    };

var dog = 
    {
        "feet": 4
    };


var superduck = $.extend({}, animal, duck);
var superdog  = $.extend({}, animal, dog);

console.log(superduck.feet);
console.log(superdog.feet);

superduck.speak();
superdog.speak();

superduck.addFriend("chicken")
superduck.addFriend("bird")

superdog.addFriend("cat")

console.log(superdog.languages);
console.log(superdog.friends);