類的四種定義方法

1.工廠模式

function Car(name, color, price) {
  var tempcar = new Object; 
  tempcar.name = name; 
  tempcar.color = color; 
  tempcar.price = price; 
  
  tempcar.getCarInfo = function () { 
  	console.log(`name: ${this.name},color: ${this.color},price: ${this.price}`); 
  }
  return tempcar;
} 

var mycar = new Car('BMW', 'red', '100000'); 
mycar.getCarInfo(); 
 

缺點：每次 new 一個物件的時候，都會重新建立一個 getCaeInfo() 函式；

2. 建構函式方式

function Car(name, color, price) { 
    this.name = name; 
    this.color = color; 
    this.price = price; 
    this.getCarInfo = function () {
        console.log(`name: ${this.name},color: ${this.color},price: ${this.price}`); 
    } 
} 

var myCar = new Car('桑塔納', 'green', '123456'); 
myCar.getCarInfo(); 
 

優點：

1. 不用建立臨時物件；

2. 不用返回臨時物件；

缺點：與‘工廠模式’相同,重複建立函式；

3.原型方式

function Car(name, color, price) { 
    Car.prototype.name = name; 
    Car.prototype.color = color; 
    Car.prototype.price = price; 
    Car.prototype.getCarInfo = function () { 
        console.log(`name: ${this.name},color: ${this.color},price: ${this.price}`); 
    } 
} 

var myCar = new Car('蘭博基尼', 'red', '10000000000'); 
myCar.getCarInfo(); 
 

優點：

1. 解決了重複建立函式的問題；

2. 可以使用 instanceof 檢驗型別 myCar instanceof Car // true

缺點： 多個例項建立的相同屬性指向同一塊記憶體；

例子：

Car.prototype.drivers = ['Tim', 'Jone']; 
myCar.drivers.push('mike'); 
console.log(myCar.drivers); // ['Tim', 'Jone', 'mike'] 

4.動態原型方式（推薦）

function Car(name, color, price, drivers) { 
    this.name = name; 
    this.color = color; 
    this.price = price; 
    this.drivers = drivers; 
}

Car.prototype.getCarInfo = function () { 
    console.log(`name: ${this.name},color: ${this.color},price: ${this.price}`); 
} 

var myCar = new Car('蘭博基尼', 'red', '10000000000', ['qaz', 'wsx']); 
myCar.drivers.push('mi'); 
console.log(myCar.drivers); // ["qaz", "wsx", "mi"] 
var myCar1 = new Car('蘭博基尼1', 'red1', '100000000001', ['qaz1', 'wsx1']); 
myCar1.drivers.push('mi1'); 
console.log(myCar1.drivers); // ["qaz1", "wsx1", "mi1"] 

思想：

類的屬性 要隨例項物件動態改變； => 動態

類的方法 要隨原型保持不變；=> 原型