状态模式

状态模式: 将事物内部的每个状态分别封装成类, 内部状态改变会产生不同行为。

优点: 用对象代替字符串记录当前状态, 状态易维护

缺点: 需编写大量状态类对象
场景 demo
某某牌电灯, 按一下按钮打开弱光, 按两下按钮打开强光, 按三下按钮关闭灯光。

//  将状态封装成不同类
const weakLight = function(){
  this.light = light
}
weakLight.prototype.press = function(){
  console.log('打开强光')
  this.light.setState(this.light.strongLight)
}
const strongLight = function(){
  this.light= light
}
strongLight.prototype.press = function(){
  console.log('关灯')
  this.light.setState(this.light.offLight)
}
const offLight = function(){
  this.light= light
}
offLight.prototype.press = function(){
  console.log('打开弱光')
  this.light.setState(this.light.weakLight)
}
 const Light = function(){
   this.weakLight = new weakLight(this)
   this.strongLight = new strongLight(this)
   this.offLight = new offLight(this)
   this.currentState = this.offLight //初始状态
 }
 Light.prototype.init = function(){
   const btn = doucment.createElement('button')
   btn.innerHTML = '按钮'
   document.body.append(btn)
   const self = this
   btn.addEventListener('click',function(){
     self.currentState.press()
   })
 }
 Light.prototype.setState = function(state){
  this.currentState = state
 }
 const light = new Light()
 light.init()

非面向对象实现的状态模式

// 借助于javascript的委托机制  可以像如下实现状态模式
const obj = {
  'weakLight': {
    press: function(){
      console.log('打开强光')
      this.currentState = obj.strongLight
    }
  },
  'strongLight': {
    press: function(){
      console.log('关灯')
      this.currentState = obj.offLight
    }
  },
  'offLight': {
    press: function(){
      console.log('打开弱光')
      this.currentState = obj.weakLight
    }
  },
}
 const Light = function(){
   this.currentState = obj.offLight
 }
 Light.prototype.init = function(){
   const btn = document.createElement('button')
   btn.innerHTML = '按钮'
   document.body.append(btn)
   const self = this
   btn.addEventListener('click',function(){
     self.currentState.press.call(self) //通过call完成委托
   })
 }
 const light = new Light()
 light.init()