JS map 函数内部的计算

Question

在下面的代码中是否有更好/简单的方法来计算 servicecost 和 gatewayCost？我正在遍历一个 json 数组以创建另一个 json 对象来更新数据库中的结果。代码工作正常，但我觉得所使用的逻辑不是一个理想的逻辑。任何简化以下代码的帮助将不胜感激。

var shippingCharge=20;
var serviceChargePercent =5;
var gstPercentOnServiceCharge=5;
var paymentGatewayPercent =2;
var cart=
[
    {
        "id": 9,
        "title": "Unero Military Classical Backpack",
        "is_featured": false,
         quantity:2,
        "is_hot": false,
        "price": 42.2,
        "sale_price": 35.89,
        "vendor": "Young shop",
        "review": 3,
        "variants": [],
    },
    {
        "id": 18,
        "title": "Samsung UHD TV 24inch",
        "is_featured": false,
         quantity:2,
        "is_hot": false,
        "price": 599,
        "sale_price": null,
        "vendor": "Robert's Store",
        "review": 4,
        "variants": [],
    }    
]

tableData = cart.map((product, index) => ({
            payment_mode: this.state.paymentMode,
            invoiceID: parseInt(lastInvoiceId) + 1,         
            productTitle: product.title,
            buyerEmailId: emailID,     `enter code here`       
            servicecost: (
                product.quantity *
                    product.price *
                    (serviceChargePercent / 100) +
                product.quantity *
                    product.price *
                    (gstPercentOnServiceCharge / 100)
            ).toFixed(2),
            gatewayCost: (
                (parseFloat((product.quantity * product.price).toFixed(2)) +
                    parseFloat(shippingCharge.toFixed(2)) +
                    parseFloat(
                        (
                            product.quantity *
                                product.price *
                                (serviceChargePercent / 100) +
                            product.quantity *
                                product.price *
                                (gstPercentOnServiceCharge / 100)
                        ).toFixed(2)
                    )) *
                (paymentGatewayPercent / 100)
            ).toFixed(2),
            
        }));