const router = new VueRouter({
 routes: [...],
 scrollBehavior (to, from, savedPosition) {
  // return 期望滾動到哪個的位置
 }
})

{ x: number, y: number }
{ selector: string, offset? : { x: number, y: number }} (offset 只在 2.6.0+ 支持)

scrollBehavior (to, from, savedPosition) {
 return { x: 0, y: 0 }
}

scrollBehavior (to, from, savedPosition) {
 if (savedPosition) {
  return savedPosition
 } else {
  return { x: 0, y: 0 }
 }
}

scrollBehavior (to, from, savedPosition) {
 if (to.hash) {
  return {
   selector: to.hash
  }
 }
}

 routes: [
  { path: '/', component: Home, meta: { scrollToTop: true }},
  { path: '/foo', component: Foo },
  { path: '/bar', component: Bar, meta: { scrollToTop: true }}
 ]

import Vue from 'vue'
import VueRouter from 'vue-router'
Vue.use(VueRouter)
const Home = { template: '<div>home</div>' }
const Foo = { template: '<div>foo</div>' }
const Bar = {
 template: `
  <div>
   bar
   <div style="height:500px"></div>
   <p id="anchor">Anchor</p>
  </div>
 `
}
// scrollBehavior:
// - only available in html5 history mode
// - defaults to no scroll behavior
// - return false to prevent scroll
const scrollBehavior = (to, from, savedPosition) => {
 if (savedPosition) {
  // savedPosition is only available for popstate navigations.
  return savedPosition
 } else {
  const position = {}
  // new navigation.
  // scroll to anchor by returning the selector
  if (to.hash) {
   position.selector = to.hash
  }
  // check if any matched route config has meta that requires scrolling to top
  if (to.matched.some(m => m.meta.scrollToTop)) {
   // cords will be used if no selector is provided,
   // or if the selector didn't match any element.
   position.x = 0
   position.y = 0
  }
  // if the returned position is falsy or an empty object,
  // will retain current scroll position.
  return position
 }
}
const router = new VueRouter({
 mode: 'history',
 base: __dirname,
 scrollBehavior,
 routes: [
  { path: '/', component: Home, meta: { scrollToTop: true }},
  { path: '/foo', component: Foo },
  { path: '/bar', component: Bar, meta: { scrollToTop: true }}
 ]
})

new Vue({
 router,
 template: `
  <div id="app">
   <h1>Scroll Behavior</h1>
   <ul>
    <li><router-link to="/">/</router-link></li>
    <li><router-link to="/foo">/foo</router-link></li>
    <li><router-link to="/bar">/bar</router-link></li>
    <li><router-link to="/bar#anchor">/bar#anchor</router-link></li>
   </ul>
   <router-view class="view"></router-view>
  </div>
 `
}).$mount('#app')

router.afterEach((to,from,next) => {
  window.scrollTo(0,0);
});