03单例模式

最简单的单例模式

class Window {
  constructor(name) {
    this.name = name;
  }
  static getInstance() {
    // 静态方法 this是Window类
    // 第一次走new window方法 ，第二次this.instance就有值，用自己的

    this.instance = this.instance || new Window
    return this.instance

  }
}
const w1 = Window.getInstance()
const w2 = Window.getInstance()
console.log(w1 === w2); //true

两个缺点：

1.调用者必须知道Window类有getInstance静态方法。

2.不能阻止调用者new Window().这样会产出多个实例对象。

透明单例

class Window {
  constructor(name) {
    this.name = name;
  }
  getName() {
    console.log(this.name);
  }
}
const CreateSingleton = (function () {
  let instance = null
  return function CreateSingleton(name) {
    instance = instance || new Window(name)
    return instance

  }

})()
const w1 = new CreateSingleton('w1') //new 可以不用
const w2 = new CreateSingleton('w2')
console.log(w1 === w2); //true

扩展透明单例：如果有多个类，而创建单例的逻辑是一样的。

class Window {
  constructor(name) {
    this.name = name;
  }
  getName() {
    console.log(this.name);
  }
}

class Dialog {
  constructor(title, content) {
    this.title = title;
    this.content = content;
  }
}

const CreateSingleton = function (Constructor) {
  let instance = null
  return function (...args) {
    instance = instance || new Constructor(...args)
    return instance

  }

}
// 创建Window单例
const CreateWindow = CreateSingleton(Window) //创建Window单例
const w1 = new CreateWindow('w1') //new 可以不用
const w2 = new CreateWindow('w2')
// 创建Dialog单例
const CreateDialog = CreateSingleton(Dialog)
const d1 = new CreateDialog('t1', 'c1')
const d2 = new CreateDialog('t2', 'c2')
console.log(d1); //Dialog { title: 't1', content: 'c1' }
console.log(d2); //Dialog { title: 't1', content: 'c1' }