用导航钩子函数
https://router.vuejs.org/zh-c...

<p id="app">
    <router-link to="/a">aaaa</router-link>
    <router-link to="/b">index</router-link>
    
    <transition :name="v">
        <router-view ></router-view>
    </transition>
            
</p>
    
        

            const router = new VueRouter({
                routes: [
                    {
                        path: '/a',
                        component: {
                            template: '<span>a</span>'
                        }
                    },
                    {
                        path: '/b',
                        component: {template: '<span>b</span>'}
                    }
                ]
            })
            
            var app = new Vue({
                el: '#app',
                data: {
                    v: 1
                },
                router，
                watch: {
                    '$route'(to,from){
                        this.v = 2;
                    }
                }
            });