Javascript

JS设计模式-状态模式

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JS设计模式-状态模式

1.原代码

假设我们期望给按钮绑定事件以实现关灯->弱光->强光->关灯的效果

按照一般性思维我们得到了以下代码

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <button id="button"></button>
  </body>
  <script>
    class Light {
      constructor(button) {
        this.button = button;
        this.currentState = "off";
      }
      initButton() {
        this.button.onclick = ()=>{
          this.pressButton()
        };
      }
      pressButton() {
        if (this.currentState === "off") {
          console.log("弱光");
          this.currentState = "weakLight";
        } else if (this.currentState === "weakLight") {
          console.log("强光");
          this.currentState = "strongLight";
        } else {
          console.log("无光/关灯");
          this.currentState = "off";
        }
      }
    }
    let light = new Light(button)
    light.initButton()
  </script>
</html>

2.原代码存在的问题

1.不符合开放封闭原则

2.胖函数

3.状态切换不明显

4.切换关系不明确

3.采用状态模式进行改进

于是我们便得到了以下代码

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <button id="button"></button>
  </body>
  <script>
    class Light{
      constructor(button){
        this.button = button
        this.offLight = new OffLight(this)
        this.weakLight = new WeakLight(this)
        this.strongLight = new StrongLight(this)
        this.currentStatus = new OffLight(this)
      }
      setStatus(newStatus){
        this.currentStatus = newStatus
      }
      initButton() {
        this.button.onclick = ()=>{
          this.currentStatus.changeState()
      };
}


    }
    class WeakLight{
      constructor(light){
        this.light = light
      }
      changeState(){
        console.log('强光');
        this.light.setStatus(this.light.strongLight)
      }
    }
    class StrongLight{
      constructor(light){
        this.light = light
      }
      changeState(){
        console.log('无光');
        this.light.setStatus(this.light.offLight)
      }
    }
    class OffLight{
      constructor(light){
        this.light = light
      }
      changeState(){
        console.log('弱光');
        this.light.setStatus(this.light.weakLight)
      }
    }
    let light = new Light(button)
    light.initButton()
  </script>
</html>

*4.采用责任链模式对原代码进行改进

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <button id="button">switch</button>
  </body>
  <script>
    function chain(fn,status){
      this.status = status
      this.fn = fn
      this.next = null
    }

    function offLight(light){
      if(light.status === 'offLight'){
        console.log('弱光');
        light.status = 'weakLight'
      }else{
        this.next.fn.call(this.next,light)
      }
    }

    function weakLight(light){
      if(light.status === 'weakLight'){
        console.log('强光');
        light.status = 'strongLight'
      }else{
        this.next.fn.call(this.next,light)
      }
    }
    function strongLight(light){
      if(light.status === 'strongLight'){
        console.log('无光');
        light.status = 'offLight'
      }else{
        this.next.fn.call(this.next,light)
      }
    }
    chain.prototype.setNextChain = function(chain){
      this.next = chain
    }
    chain.prototype.changeStatus = function(){
      this.fn()
    }

    let light = new chain(function(){this.next.fn.call(this.next,this)},'offLight')
    let offlight = new chain(offLight,'offLight')
    let weaklight = new chain(weakLight,'weakLight')
    let stronglight = new chain(strongLight,'strongLight')


    light.setNextChain(offlight)
    offlight.setNextChain(weaklight)
    weaklight.setNextChain(stronglight)


    button.onclick = ()=>{
      light.changeStatus()
    }

  </script>
</html>
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