Prototypal inheritance

proto.js

// Prototypal inheritance example
// Checked on Node v16.14.2
assert = require('assert')

// A cat goes 'meow'
class Cat {
  goes() {
    return 'meow'
  }
}
fluffy = new Cat()
assert(fluffy.goes(), 'meow')
// So far, so Java

// Previous common alternative pattern to ES6 class
// for object inheritance - use a prototype object
Dog = {
  goes: function() {
    return 'woof'
  }
}
spot = Object.create(Dog)
assert.equal(spot.goes(), 'woof')
// Nothing terribly odd up to here

// Prototype reassignment 
// Magic trick, turn fluffy into a dog
fluffy.__proto__ = Dog
assert.equal(fluffy.goes(), 'woof')

// Dynamic augmentation
// Magic trick, teach all dogs to sing
Dog.sing = () => "We'll... meet again!"
// Fluffy can now sing!
assert.ok(fluffy.sing().startsWith('We'))