Analyse d'un exemple de comportement de défilement de Vue

<p id="app">
  <h1>滚动行为</h1>
  <ul>
    <li><router-link to="/">首页</router-link></li>
    <li><router-link to="/foo">导航</router-link></li>
    <li><router-link to="/bar">关于</router-link></li>
    <li><router-link to="/bar#an1">红色页面</router-link></li>
    <li><router-link to="/bar#an2">蓝色页面</router-link></li>
  </ul>
  <router-view></router-view>
</p>
<script>
  var Home = {
    template:"<p>home</p>"
  }
  var Foo = {
    template:"<p>foo</p>"
  }
  var Bar = {
    template:
      `
        <p>
          bar
          <p style="height:500px;background: yellow;"></p>
          <p id="an1" style="height:500px;background: red;">红色页面</p>
          <p id="an2" style="height:300px;background: blue;">蓝色页面</p>
        </p>
      `
  }

  var router = new VueRouter({
    mode:"history",
    //控制滚动位置
    scrollBehavior (to, from, savedPosition) {
      //判断如果滚动条的位置存在直接返回到当前位置，否者返回到起点
      if (savedPosition) {
        return savedPosition
      } else {
        if (to.hash) {
          return {selector: to.hash}
        }
      }
    },
    routes:[
      {
        path:"/",component:Home
      },
      {
        path:"/foo",component:Foo
      },
      {
        path:"/bar",component:Bar
      }
    ]
  });
  var vm = new Vue({
    el:"#app",
    router
  });
</script>