还可以基于当前路由与目标路由的变化关系，动态设置过渡效果：

<!-- 使用动态的 transition name -->
<transition :name="transitionName">
  <router-view></router-view>
</transition>

// 接着在父组件内

// watch $route 决定使用哪种过渡
watch: {
  '$route' (to, from) {
    const toDepth = to.path.split('/').length
    const fromDepth = from.path.split('/').length
    this.transitionName = toDepth < fromDepth ? 'slide-right' : 'slide-left'
  }
}

实例：

import Vue from 'vue'
import VueRouter from 'vue-router'

Vue.use(VueRouter)

const Home = {
  template: `
    <div class="home">
      <h2>Home</h2>
      <p>hello</p>
    </div>
  `
}

const Parent = {
  data () {
    return {
      transitionName: 'slide-left'
    }
  },
  beforeRouteUpdate (to, from, next) {
    const toDepth = to.path.split('/').length
    const fromDepth = from.path.split('/').length
    this.transitionName = toDepth < fromDepth ? 'slide-right' : 'slide-left'
    next()
  },
  template: `
    <div class="parent">
      <h2>Parent</h2>
      <transition :name="transitionName">
        <router-view class="child-view"></router-view>
      </transition>
    </div>
  `
}

const Default = { template: '<div class="default">default</div>' }
const Foo = { template: '<div class="foo">foo</div>' }
const Bar = { template: '<div class="bar">bar</div>' }

const router = new VueRouter({
  mode: 'history',
  base: __dirname,
  routes: [
    { path: '/', component: Home },
    { path: '/parent', component: Parent,
      children: [
        { path: '', component: Default },
        { path: 'foo', component: Foo },
        { path: 'bar', component: Bar }
      ]
    }
  ]
})

new Vue({
  router,
  template: `
    <div id="app">
      <h1>Transitions</h1>
      <ul>
        <li><router-link to="/">/</router-link></li>
        <li><router-link to="/parent">/parent</router-link></li>
        <li><router-link to="/parent/foo">/parent/foo</router-link></li>
        <li><router-link to="/parent/bar">/parent/bar</router-link></li>
      </ul>
      <transition name="fade" mode="out-in">
        <router-view class="view"></router-view>
      </transition>
    </div>
  `
}).$mount('#app')