transition這個標簽上除了綁定name還可以綁定before-enter，enter，before-leave，leave

<transition name="fade"
                @before-enter="beact"
                @enter="eact"
                @before-leave="blact"
                @leave="lact"
                > 
<div v-if="show" >hello world</div>
</transition>

methods:{
                    change:function(){
                        
 
this.show=!this.show
                    },
                    beact:function(el){
                        el.style.color=‘red‘
                    },
                    eact:function(el){
                        setTimeout(()=>{
                            el.style.color=‘green‘
                            done()
                        },
 
2000)
                        
                    },
                    blact:function(el){
                        //用法
                        Velocity(el,{
                            opacity:1
                        },{
                            duration:1000,
                            complete:done()
                            })
                    },
                    lact:function(el){
                        
                    }
}
 

Vue的transition的js的鉤子函數