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职责链模式

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职责链模式：使多个对象都有机会处理请求，从而避免请求的发送者和接收者之间得到耦合关系，将这些对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止

灵活可拆分的职责链结点

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let order500 = function(orderType,pay,stock){
       if(orderType === 1 && pay===true){
           console.log('500元定金，100元优惠')
       }else{
           return 'nextSuccessor'
       }
   }
   let order200 = function(orderType,pay,stock){
       if(orderType === 2 && pay === true){
           console.log('200元定金，50元优惠')
       }else{
           return 'nextSuccessor'
       }
   }
   let orderNormal = function(orderType,pay,stock){
       if(stock>0){
           console.log('普通购买，无优惠')
       }else{
           console.log('库存不足')
       }
   }
   let Chain = function(fn){
       this.fn = fn;
       this.successor = null
   }
   Chain.prototype.setNextSuccessor = function(successor){
       return this.successor = successor
   }
   Chain.prototype.passResquest = function(){
       let ret = this.fn.apply(this,arguments)
       //console.log(ret) 
       if(ret === 'nextSuccessor'){            
           return this.successor && this.successor.passResquest.apply(this.successor,arguments)
       }
       return ret
   }
   let chainOrder500 = new Chain(order500)//500元定金，100元优惠
   let chainOrder200 = new Chain(order200)
   let chainOrderNormal = new Chain(orderNormal)
   chainOrder500.setNextSuccessor(chainOrder200)
   chainOrder200.setNextSuccessor(chainOrderNormal)
   chainOrder500.passResquest(1,true,500)//500元定金，100元优惠
   chainOrder500.passResquest(2,true,500)//走nextSuccessor,200元定金，50元优惠
   chainOrder500.passResquest(3,true,500)//继续nextSuccessor,普通购买，无优惠
   chainOrder500.passResquest(1,false,0)//一直nextSuccessor到库存不足

当要加入一个结点：

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let order300 = function(){
    ...
}
chainOrder300 = new Chain(order300)
chainOrder500.setNextSuccessor(chainOrder300)
chainOrder300.setNextSuccessor(chainOrder200)

AOP模式实现职责链：

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let order500 = function(orderType,pay,stock){
        if(orderType === 1 && pay===true){
            console.log('500元定金，100元优惠')
        }else{
            return 'nextSuccessor'
        }
    }
    let order200 = function(orderType,pay,stock){
        if(orderType === 2 && pay === true){
            console.log('200元定金，50元优惠')
        }else{
            return 'nextSuccessor'
        }
    }
    let orderNormal = function(orderType,pay,stock){
        if(stock>0){
            console.log('普通购买，无优惠')
        }else{
            console.log('库存不足')
        }
    }
Function.prototype.after = function(fn){
        let self = this
        return function(){
            let ret = self.apply(this,arguments)
            if(ret === 'nextSuccessor'){
                return fn.apply(this,arguments)
            }
            return ret;
        }
    }
    let order = order500.after(order200).after(orderNormal)
    order(1,true,500)
    order(2,true,500)
    order(1,false,500)