Love thy code!

renderOrderSummary.js

// Render HTML code for an order summary
function order_summary(order_object) {
    var price = 0,
        tax = 0,
        subtotal = '',
        html = '';
	
    switch (order_object.price_level) {
        case 'free':
            // Do nothing, default is 0!
            break;
        case 'discount':
            price = order_object.price - (order_object.discount_percentage * order_object.price);;
            break;
        case 'sale':
            price =  order_object.price - order_object.markdown;
            break;
        default:
            price = order_object.price;
    }

    tax = (order.taxes_applicable == true) ? order_object.taxes : 0;
    subtotal = (price === 0) ? 'This order is free' : price;

    html += "<p> Product:  " + order_object.product_name  + "</p>";
    html += "<p> Subtotal: $" + subtotal + "</p>";
    html += "<p> Tax: $" + tax + "</p>";
    html += "<p> Order Total: $" + (price + tax) + "</p>";
    
    document.write("<h1> Order summary </h1>" + html);
}