app.js

import Vue from 'vue'
import VueRouter from 'vue-router'
import App from './app.vue'
import ViewA from './view-a.vue'
import ViewB from './view-b.vue'

Vue.use(VueRouter)

const router = new VueRouter()

router.map({
  '/a': { component: ViewA },
  '/b': { component: ViewB }
})

router.start(App, '#app')

app.vue

<template>
  <div>
    <h1>This is the layout that won't change</h1>
    <router-view><!-- matched component renders here --></router-view>
  </div>
</template>