如何在不影响其他函数的前提下，避免空值/0值触发折扣计算

当前代码在「Deadline (months)」输入框为空或值为0时，会默认应用20%折扣，需要调整为这种情况跳过折扣计算。以下是修改方案：

关键修改点 #

• 优化months参数的解析逻辑，处理空值和0的情况
• 调整getDiscountPercent函数，当months为0、空或无效值时返回0（无折扣）

修改后的完整代码 #

//Dropdown list calculation//
var service_prices = new Array();
service_prices["0"] = 0;
service_prices["1500"] = 1500;
service_prices["4000"] = 4000;
service_prices["8000"] = 8000;

//^gives me value of each drop down list item
function getServicePrice() {
  var serviceOptionPrice = 0;
  var form = document.forms["formulario"];
  var selectedOption = form.querySelector("#servicePrice");
  if (service_prices[selectedOption.value]) {
    serviceOptionPrice = service_prices[selectedOption.value];
  }
  return serviceOptionPrice;
}

//checkbox calculation//
function extraPrices() {
  var extraPrices = 0;
  var form = document.forms["formulario"];
  var selectedBoxes = form.querySelectorAll("#selectedBox");
  selectedBoxes.forEach(box => {
    if (box.checked == true) {
      extraPrices += 400;
    }
  })
  //returns me value of each marked checkbox (all of them == 400)
  return extraPrices;
}

//Calculate how much is going to be removed from the final Value
const getDiscountPercent = months => {
  // 当months为0、空或无效值时，返回0（无折扣）
  if (!months || months <= 0) return 0;
  return months < 4 ? months * 0.05 : 0.2;
};

const getTotal = (servicePrice, extraPrice, months) => {
  const subtotal = servicePrice + extraPrice;
  const discountPercent = getDiscountPercent(months);
  return subtotal - (subtotal * discountPercent);
};

//Returns me what's gonna be subtracted from final value
function Total() {
  // 解析输入值，空值或非数字会转为NaN
  var months = parseInt(document.querySelector('#months').value);
  // 处理NaN的情况，转为0
  months = isNaN(months) ? 0 : months;
  
  var subtotal = getServicePrice() + extraPrices();
  var totalFinal = subtotal - (subtotal * getDiscountPercent(months));
  document.getElementById("result").value = "€" + totalFinal ;
}
// 注意：totalFinal是Total函数内部变量，外部无法直接访问，这里会报错，建议移除或放在函数内
// console.log(totalFinal)

修改说明 #

1. getDiscountPercent函数：新增判断逻辑，当months为0、空值或无效值时直接返回0，确保无折扣应用。
2. Total函数：
   • 处理parseInt解析空字符串得到NaN的问题，将NaN转为0
   • 简化计算逻辑，先计算小计，再应用折扣
   • 移除了外部无法访问的console.log(totalFinal)，避免报错

内容的提问来源于stack exchange，提问作者ConsoleDotLogMe