在JS中創建對象會習慣的使用 new 關鍵字和類構造函數（當然主要還是對象字面量），問題在于這樣會導致兩個類之間產生依賴性。
工廠模式就是一種有助于消除兩個類依賴性的模式。
- 簡單工廠模式：使用一個類（通常為單體）來生成實例。
- 復雜工廠模式：使用子類來決定一個成員變量應該是哪個具體的類的實例。
## 簡單工廠模式
```js
let ComputerFactory = function(){}
function MacComputer() {}
function WinComputer() {}
ComputerFactory.prototype = {
makeProduct: function (model) {
let product
switch (model) {
case "mac":
product = new MacComputer()
break
case "win":
product = new WinComputer()
break
default:
break
}
return product;
}
}
let factory = new ComputerFactory()
let mac = factory.makeProduct('mac')
let win = factory.makeProduct('win')
```
## ES6
```js
class Computer {
constructor () {
this.product = 'Computer'
}
}
class MacComputer extends Computer {
constructor () {
super()
this.name = 'MacComputer'
}
}
class WinComputer extends Computer {
constructor () {
super()
this.name = 'WinComputer'
}
}
function ComputerFactory (param) {
let product = null
switch (param) {
case 'mac':
product = new MacComputer()
break
case 'win':
product = new WinComputer()
break
default:
break
}
return product
}
let mac = ComputerFactory('mac')
let win = ComputerFactory('win')
```
