Strategy.js

function baseStrategy(amount)
{
    return amount;
}

function premiumStrategy(amount)
{
    return amount * 0.85;
}

function platinumStrategy(amount)
{
    return amount * 0.65;
}

class AutoCart
{
    constructor(discount)
    {
        this.discount = discount;
        this.amount = 0;
    }
    
    checkout()
    {
        return this.discount(this.amount);
    }
    
    setAmount(amount)
    {
        this.amount = amount;
    }
}

const baseCustomer = new AutoCart(baseStrategy);
const premiumCustomer = new AutoCart(premiumStrategy);
const platinumCustomer = new AutoCart(platinumStrategy);

baseCustomer.setAmount(50000);
console.log(baseCustomer.checkout());

premiumCustomer.setAmount(50000);
console.log(premiumCustomer.checkout());

platinumCustomer.setAmount(50000);
console.log(platinumCustomer.checkout());