Combine Function into Transform

練習用的 REPL

// 這是 reading 的資料結構
reading = {customer: "ivan", quantity: 10, month: 5, year: 2017};

// 三個呼叫端都要計算 baseCharge，但命名不見得一樣，甚至計算方法也在各地重複了

// client 1
const aReading = acquireReading();
const baseCharge = baseRate(aReading.month, aReading.year) * aReading.quantity;

// client 2
const aReading = acquireReading();
const base = (baseRate(aReading.month, aReading.year) * aReading.quantity);
const taxableCharge = Math.max(0, base - taxThreshold(aReading.year));

// client 3
const aReading = acquireReading();
const basicChargeAmount = calculateBaseCharge(aReading);

function calculateBaseCharge(aReading) {
  return  baseRate(aReading.month, aReading.year) * aReading.quantity;
}

先做個 transform function，單純回傳複製後的物件。

function enrichReading(original) {
    const result = _.cloneDeep(original);
    return result;
}

// client 3 比較單純，先套用

// client 3
const rawReading = acquireReading();        // 名字改一下
const aReading = enrichReading(rawReading); // 先用上 transform function
const basicChargeAmount = calculateBaseCharge(aReading);

然後把 calculateBaseCharge 移入 transform function。

function enrichReading(original) {
  const result = _.cloneDeep(original);
  result.baseCharge = calculateBaseCharge(result);
  return result;
}

// client 3
const rawReading = acquireReading();
const aReading = enrichReading(rawReading);
const basicChargeAmount = aReading.baseCharge;  // 這邊就可以換成取值


// client 1
const rawReading = acquireReading();
const aReading = enrichReading(rawReading);     // 這邊就可以換成取值
const baseCharge = aReading.baseCharge;

// client 2 毛比較多

// 先套用 transform function
const rawReading = acquireReading();
const aReading = enrichReading(rawReading);
const base = (baseRate(aReading.month, aReading.year) * aReading.quantity);
const taxableCharge = Math.max(0, base - taxThreshold(aReading.year));

// baseCharge 改成取值
const rawReading = acquireReading();
const aReading = enrichReading(rawReading);
const base = aReading.baseCharge;   // 這邊就可以換成取值
const taxableCharge = Math.max(0, base - taxThreshold(aReading.year));

// 其他地方也改成取值
const rawReading = acquireReading();
const aReading = enrichReading(rawReading);
const taxableCharge = Math.max(0, aReading.baseCharge - taxThreshold(aReading.year));   // 這邊就可以換成取值

繼續把 taxableCharge 移入 transform function。

function enrichReading(original) {
    const result = _.cloneDeep(original);
    result.baseCharge = calculateBaseCharge(result);
    result.taxableCharge = Math.max(0, result.baseCharge - taxThreshold(result.year));  // 把 taxableCharge 也納進來
    return result;
}

// 這是剛剛的
const rawReading = acquireReading();
const aReading = enrichReading(rawReading);
const taxableCharge = Math.max(0, aReading.baseCharge - taxThreshold(aReading.year));

// 可以再變成這樣
const rawReading = acquireReading();
const aReading = enrichReading(rawReading);
const taxableCharge = aReading.taxableCharge;   // 這邊就可以換成取值