//router.js
import Vue from 'vue';
import Router from 'vue-router';
Vue.use(Router);

const router = new Router({
 mode: 'hash',
 routes: [
 {
  path: '/',
  name: 'home',
  component: () =>
  import('./views/Home.vue'),
  meta: {
  title: '首页',
  keepAlive: false //此组件不需要被缓存
  }
 },
 {
  path: '/pageA',
  name: 'pageA',
  component: () =>
   import('./views/pageA.vue'),
  meta: {
  title: 'pageA',
  keepAlive: true,
  isBack: false
  }
 },
 {
  path: '/pageB',
  name: 'pageB',
  component: () =>
   import('./views/pageB.vue'),
  meta: {
  title: 'pageB',
  keepAlive: true,
  isBack: false
  }
 },
 {
  path: '/pageC',
  name: 'pageC',
  component: () =>
   import('./views/pageC.vue'),
  meta: {
  title: 'pageC',
  keepAlive: false
  }
 }
 ]
});
export default router;
//pageA.vue
<template>
 <div class="page-a">
  <h1>pageA</h1>
  <div>
   <div class="item" v-for="item in items" @click="goPageB">
    {{ item }}
   </div>
  </div>
  <h1 @click="goPageB">go pageB</h1>
 </div>
</template>

<script>
 export default {
  name: 'PageA',
  data() {
   return {
    msg: "我是PageA页面",
    items: Array.from({length:50}, (v,k) => k),
    data: "",
    scrollTop: 0
   };
  },
  beforeRouteEnter(to, from, next) {
   if(from.name == 'pageB'){
    to.meta.isBack = true;
   }

   next();
  },
  mounted() {
   console.log('mounted....');
   // this指向组件的实例，$el指向当前组件的DOM元素
   const $el = this.$el;
   //滚动事件
   $el.addEventListener("scroll", () => {
    //记录位置
    this.scrollTop = $el.scrollTop;
   });
  },
  activated() {
   if(!this.$route.meta.isBack){
    // 如果isBack是false，表明需要获取新数据，否则就不再请求，直接使用缓存的数据
    this.getData();
   } else {
    //恢复滚动条高度
    if(this.scrollTop) {
     setTimeout(() => {
      this.$el.scrollTop = this.scrollTop;
     }, 100);
    }
   }
   // 恢复成默认的false，避免isBack一直是true
   this.$route.meta.isBack = false;

  },
  methods: {
   getData() {
    // getData方法，模拟从后台请求数据
    this.data = "数据";
    console.log('get data')
   },
   goPageB(){
    this.$router.push({ path: "/pageB" });
   },
   back() {
    this.$router.push({ path: "/" });
   }
  },
 }
</script>
<style>
 .page-a {
  height: 100vh;
  overflow-y: auto;
 }
 .item {
  margin: 5px;
  padding: 10px;
  background: #ccc;
 }
</style>