Data privacy and extension with Javascript!

oop.js

var Person = function (firstName, lastName) {
    function privateGetName() {
        return `${firstName} ${lastName}`;
    }
    return {
        getName() {
            return privateGetName();
        },
        speak() {
            console.log('Hello!');
        }
    };
};

var SalesPerson = function (firstName, lastName) {
    return Object.assign(Object.create(Person(firstName, lastName)), {
        sell() {
            console.log('That\'ll be $5!');
        },

        // Override
        speak() {
            Object.getPrototypeOf(this).speak.call(this);
            console.log(`My name is ${this.getName()}`);
        }
    });
};