SOURCE

const User = {
  template: `<div>User {{ $route.params.id }}</div>`,
  mounted() {
      console.log('2222222222', this.$root.$options.components)
  }
  
}

const router = new VueRouter({
  routes: [
    { path: '/user/:id', component: User }
  ]
})
Vue.component('test', {
    template: '<div>2222222222</div>'
})
console.log('2222222222', Vue.options.components)
const app = new Vue({ router }).$mount('#app')

<script src="https://unpkg.com/vue/dist/vue.js"></script>
<script src="https://unpkg.com/vue-router/dist/vue-router.js"></script>

<div id="app">
  <p>
    <router-link to="/user/foo">/user/foo</router-link>
    <router-link to="/user/bar">/user/bar</router-link>
  </p>
  <router-view></router-view>
</div>

a.router-link-active {
  color: #f66;
}
li.router-link-active a {
  color: #f66;
}