Introduction to JavaScript Programming Course from Front-End Master. https://frontendmasters.com/courses/javascript-basics/

exercise.js

/* Exercise from https://github.com/getify/You-Dont-Know-JS/blob/master/up%20&%20going/ch1.md#practice */
(function() {
    const TAX_RATE = 0.08;
    const PHONE_PRICE = 99.99;
    const ACCESORY_PRICE = 9.99;
    const SPENDING_THRESHOLD = 200;

    var accountBalance = 303.91;
    var amount = 0;

    function calculateTax(amount, taxRate) {
        return amount * taxRate;
    }

    function numberFormat(number) {
        return "$" + number.toFixed(2);
    }

    while (amount < accountBalance) {
        amount += PHONE_PRICE;

        if (amount < SPENDING_THRESHOLD) {
            amount += ACCESORY_PRICE;
        }
    }
    
    amount += calculateTax(amount, TAX_RATE);

    console.log("Calculated Purchase: " + numberFormat(amount));

    if (amount <= accountBalance) {
        console.log("You can afford it!");
    } else {
        console.log("You cannot afford it!");
    }
}());