Introduce Parameter Object

練習用的 REPL

const station = { name: "ZB1",
                  readings: [
                    {temp: 47, time: "2016-11-10 09:10"},
                    {temp: 53, time: "2016-11-10 09:20"},
                    {temp: 58, time: "2016-11-10 09:30"},
                    {temp: 53, time: "2016-11-10 09:40"},
                    {temp: 51, time: "2016-11-10 09:50"},
                  ]
                };

function readingsOutsideRange(station, min, max) {
    return station.readings
        .filter(r => r.temp < min || r.temp > max);
}

// 某個呼叫端可能會這樣呼叫
alerts = readingsOutsideRange(station,
    operatingPlan.temperatureFloor,
    operatingPlan.temperatureCeiling);

min、max 是一組的，做成 Parameter Object。

class NumberRange { // Parameter Object，常常是 Value Object
  constructor(min, max) {
    this._data = {min: min, max: max};
  }
  get min() {return this._data.min;}
  get max() {return this._data.max;}
}

function readingsOutsideRange(station, min, max, range) {
    return station.readings
        .filter(r => r.temp < min || r.temp > max);
}

alerts = readingsOutsideRange(station,
    operatingPlan.temperatureFloor,
    operatingPlan.temperatureCeiling,
    null); // 多加上 null，在 JavaScript 內，呼叫端應該不會受影響（但不總是 100% 安全，得跑測試）

// 在使用 Parameter Object 後，可以傳入
const range = new NumberRange(operatingPlan.temperatureFloor, operatingPlan.temperatureCeiling);
alerts = readingsOutsideRange(station,
    operatingPlan.temperatureFloor,
    operatingPlan.temperatureCeiling,
    range);

function readingsOutsideRange(station, min, range) { // 先移除參數 max
  return station.readings
    .filter(r => r.temp < min || r.temp > range.max);
}

const range = new NumberRange(operatingPlan.temperatureFloor, operatingPlan.temperatureCeiling);
alerts = readingsOutsideRange(station,
  operatingPlan.temperatureFloor,
  range);

function readingsOutsideRange(station, range) { // 再移除參數 min
  return station.readings
    .filter(r => r.temp < range.min || r.temp > range.max);
}

const range = new NumberRange(operatingPlan.temperatureFloor, operatingPlan.temperatureCeiling);
alerts = readingsOutsideRange(station, range);

把判斷是否在區間內的行為，搬回 Parameter Object 內。

function readingsOutsideRange(station, range) {
    return station.readings
        .filter(r => r.temp < range.min || r.temp > range.max);
}

class NumberRange {
  constructor(min, max) {
    this._data = {min: min, max: max};
  }
  get min() {return this._data.min;}
  get max() {return this._data.max;}
  contains(arg) {return (arg >= this.min && arg <= this.max);} // 將 filter 內容抽成 contains
}

function readingsOutsideRange(station, range) {
    return station.readings
        .filter(r => !range.contains(r.temp));  // 使用 method 加強語意
}