用transition包裹要加动画的组件，给transition加一个name属性，类似fadetog,用tadetog加每个过渡的六个状态
<transition name='fadetog'><cpt1 v-show='onOff'></cpt1></transition>
.fadetog-enter{
opacity:0
}
.fadetog-enter-active{
transition:0.5s;
}
.fadetog-enter-to{
opacity:1
}
.fadetog-leave{
opacity:1
}
.fadetog-leave-active{
transition:0.5s;
}
.fadetog-leave-to{
opacity:0
}