1. //解读  this.$set(object,key,value)   
    2. //案例
    3. let list =[{age:'1',name:'小丑'},{age:'1',name:'小丑'},{age:'1',name:'小丑'},.{age:'1',name:'小丑'},{age:'1',name:'小丑'}]
    5. this.$set(list[index], 'showSub', false)
    7. //给list[index]添加一个showSub属性,值为false