User.js

class User {
    constructor(firstName, lastName) {
        this._firstName = firstName
        this._lastName = lastName
    }

    sayHello() {
        console.log(`L'utilisateur ${this._firstName} ${this._lastName} vous dit bonjour`)
    }
}

const userWithUsername = (User, username) => {
    User._username = username
    User.sayHello = () => {
        console.log(`${User._username} vous dit bonjour`)
    }

    return User
}

// L'utilisateur initialement
const OriginalUser = new User('Thomas', 'Dimnet')
OriginalUser.sayHello()

// L'utilisateur décoré
const DecoratedUser = userWithUsername(new User('Antoine', 'Dubois'), 'adubois')
DecoratedUser.sayHello()