Split Phase

練習用的 REPL

計算價格、計算運費感覺是兩個階段。

function priceOrder(product, quantity, shippingMethod) {
    const basePrice = product.basePrice * quantity;     // 基本價格
    const discount = Math.max(quantity - product.discountThreshold, 0) *
        product.basePrice * product.discountRate;       // 計算折扣
    const shippingPerCase = (basePrice > shippingMethod.discountThreshold) ?
        shippingMethod.discountedFee : shippingMethod.feePerCase; // 每件運費
    const shippingCost = quantity * shippingPerCase;    // 總運費
    const price = basePrice - discount + shippingCost;  // 訂單最後價格
    return price;
}

先把計算運費的部分抽出來。

function priceOrder(product, quantity, shippingMethod) {
    const basePrice = product.basePrice * quantity;
    const discount = Math.max(quantity - product.discountThreshold, 0) *
        product.basePrice * product.discountRate;
    const price = applyShipping(basePrice, shippingMethod, quantity, discount);
    return price;
}

// 先把運費計算的部分抽出來
function applyShipping(basePrice, shippingMethod, quantity, discount) {
    const shippingPerCase = (basePrice > shippingMethod.discountThreshold) ?
        shippingMethod.discountedFee : shippingMethod.feePerCase;
    const shippingCost = quantity * shippingPerCase;
    const price = basePrice - discount + shippingCost;
    return price;
}

parameter 好多，現實狀況下可能會更多。

function priceOrder(product, quantity, shippingMethod) {
  const basePrice = product.basePrice * quantity;
  const discount = Math.max(quantity - product.discountThreshold, 0)
          * product.basePrice * product.discountRate;
  const priceData = {}; // 引入中介變數
  const price =  applyShipping(priceData, basePrice, shippingMethod, quantity, discount);
  return price;
}

// 傳入，但不使用
function applyShipping(priceData, basePrice, shippingMethod, quantity, discount) {
  const shippingPerCase = (basePrice > shippingMethod.discountThreshold)
          ? shippingMethod.discountedFee : shippingMethod.feePerCase;
  const shippingCost = quantity * shippingPerCase;
  const price =  basePrice - discount + shippingCost;
  return price;
}

把參數一一收進 priceData，先收 basePrice。

function priceOrder(product, quantity, shippingMethod) {
  const basePrice = product.basePrice * quantity;
  const discount = Math.max(quantity - product.discountThreshold, 0)
          * product.basePrice * product.discountRate;
  const priceData = {basePrice: basePrice}; // 把 basePrice 放進入
  const price =  applyShipping(priceData, shippingMethod, quantity, discount);  // 就可以把 basePrice 刪掉了
  return price;
}

function applyShipping(priceData, shippingMethod, quantity, discount) {
  const shippingPerCase = (priceData.basePrice > shippingMethod.discountThreshold)
          ? shippingMethod.discountedFee : shippingMethod.feePerCase;
  const shippingCost = quantity * shippingPerCase;
  const price =  priceData.basePrice - discount + shippingCost;
  return price;
}

再收 quantity。

function priceOrder(product, quantity, shippingMethod) {
  const basePrice = product.basePrice * quantity;
  const discount = Math.max(quantity - product.discountThreshold, 0)
          * product.basePrice * product.discountRate;
  const priceData = {basePrice: basePrice, quantity: quantity}; // 接著把 quantity 加入
  const price =  applyShipping(priceData, shippingMethod, discount);    // 就可以把 quantity 刪掉了
  return price;
}

function applyShipping(priceData, shippingMethod, discount) {
  const shippingPerCase = (priceData.basePrice > shippingMethod.discountThreshold)
          ? shippingMethod.discountedFee : shippingMethod.feePerCase;
  const shippingCost = priceData.quantity * shippingPerCase;
  const price =  priceData.basePrice - discount + shippingCost;
  return price;
}

再收 discount。

function priceOrder(product, quantity, shippingMethod) {
  const basePrice = product.basePrice * quantity;
  const discount = Math.max(quantity - product.discountThreshold, 0)
          * product.basePrice * product.discountRate;
  const priceData = {basePrice: basePrice, quantity: quantity, discount:discount};  // 同樣把 discount 加上去
  const price =  applyShipping(priceData, shippingMethod);  // 就可以把 discount 刪掉了
  return price;
}

function applyShipping(priceData, shippingMethod) {
  const shippingPerCase = (priceData.basePrice > shippingMethod.discountThreshold)
          ? shippingMethod.discountedFee : shippingMethod.feePerCase;
  const shippingCost = priceData.quantity * shippingPerCase;
  const price =  priceData.basePrice - priceData.discount + shippingCost;
  return price;
}

運費的部分處理好了，接下來是計算價格。

function priceOrder(product, quantity, shippingMethod) {
  const priceData = calculatePricingData(product, quantity);    // 這地方就可以直接用
  const price =  applyShipping(priceData, shippingMethod);      // 看起來直觀許多，也不用理會計算細節
  return price;
}

// 然後把這部分抽出來變成 function
function calculatePricingData(product, quantity) {
  const basePrice = product.basePrice * quantity;
  const discount = Math.max(quantity - product.discountThreshold, 0)
          * product.basePrice * product.discountRate;
  return {basePrice: basePrice, quantity: quantity, discount:discount};
}

function applyShipping(priceData, shippingMethod) {
  const shippingPerCase = (priceData.basePrice > shippingMethod.discountThreshold)
          ? shippingMethod.discountedFee : shippingMethod.feePerCase;
  const shippingCost = priceData.quantity * shippingPerCase;
  const price =  priceData.basePrice - priceData.discount + shippingCost;
  return price;
}

兩階段計算大致完成。

function priceOrder(product, quantity, shippingMethod) {
  const priceData = calculatePricingData(product, quantity);
  return applyShipping(priceData, shippingMethod);                          // 多個 price 有點多餘，刪除
}

function calculatePricingData(product, quantity) {
  const basePrice = product.basePrice * quantity;
  const discount = Math.max(quantity - product.discountThreshold, 0)
          * product.basePrice * product.discountRate;
  return {basePrice: basePrice, quantity: quantity, discount:discount};
}

function applyShipping(priceData, shippingMethod) {
  const shippingPerCase = (priceData.basePrice > shippingMethod.discountThreshold)
          ? shippingMethod.discountedFee : shippingMethod.feePerCase;
  const shippingCost = priceData.quantity * shippingPerCase;
  return priceData.basePrice - priceData.discount + shippingCost;           // 多個 price 有點多餘，刪除
}