const Car = function() { }
Car.prototype.getPrice = function() {return new Error('抽象方法不能調用')}

/**
* 實現subType類對工廠類中的superType類型的抽象類的繼承
* @param subType 要繼承的類
* @param superType 工廠類中的抽象類type
*/
const VehicleFactory = function(subType, superType) {
 if (typeof VehicleFactory[superType] === 'function') {
  function F() {
   this.type = '車輛'
  } 
  F.prototype = new VehicleFactory[superType]()
  subType.constructor = subType
  subType.prototype = new F()        // 因為子類subType不僅需要繼承superType對應的類的原型方法，還要繼承其對象屬性
 } else throw new Error('不存在該抽象類')
}
VehicleFactory.Car = function() {
 this.type = 'car'
}
VehicleFactory.Car.prototype = {
 getPrice: function() {
  return new Error('抽象方法不可使用')
 },
 getSpeed: function() {
  return new Error('抽象方法不可使用')
 }
}
const BMW = function(price, speed) {
 this.price = price
 this.speed = speed
}
VehicleFactory(BMW, 'Car')    // 繼承Car抽象類
BMW.prototype.getPrice = function() {    // 覆寫getPrice方法
 console.log(`BWM price is ${this.price}`)
}
BMW.prototype.getSpeed = function() {
 console.log(`BWM speed is ${this.speed}`)
}
const baomai5 = new BMW(30, 99)
baomai5.getPrice()             // BWM price is 30
baomai5 instanceof VehicleFactory.Car    // true