keepalive 跳转到某个页面缓存 否则不缓存 缓存浏览的位置

export const KeepaliveListMixin = {
/**
 *   两个路由守卫  实现 从详情返回到列表 列表页面缓存  否则就不缓存
 */
beforeRouteEnter (to, from, next) {
  to.meta.keepAlive = true;
  next()
},
beforeRouteLeave (to, from, next) {
  if (to.name == "DetailStore") { //这里的路径是要跳转的需要缓存的路径
    from.meta.keepAlive = true;
  } else {
    let Vnode = this.$vnode;
    let parentVnode = Vnode && Vnode.parent;
    if (parentVnode && parentVnode.componentInstance && parentVnode.componentInstance.cache) {
      var key = Vnode.key == null ? Vnode.componentOptions.Ctor.cid + (Vnode.componentOptions.tag ? `::${Vnode.componentOptions.tag}` : '') : Vnode.key;
      var cache = parentVnode.componentInstance.cache;
      var keys = parentVnode.componentInstance.keys;
      if (cache[key]) {
        this.$destroy();
        if (keys.length) {
          var index = keys.indexOf(key);
          if (index > -1) {
            keys.splice(index, 1);
          }
        }
        cache[key] = null;
      }
    }
  }
//记录离开时的位置 start
  let position = document.documentElement.scrollTop || document.body.scrollTop
  from.meta.savedPosition = position
//记录离开时的位置 end
  next();
  },
}

const scrollBehavior = function scrollBehavior (to, from, savedPosition) {
 // if (savedPosition) {
    //return savedPosition;
 // }else {
     // return { x: 0, y: 0 }
   //}
//需要返回一个promise 否则滚动条的位置 和滚动条的值不一样
return new Promise((resolve) => {
    setTimeout(() => {
      if (savedPosition ) {
        return savedPosition
      }else {
        return { x: 0, y: 0 }
      }
    },0)
  })
};
const router = new Router({
  routes,
  scrollBehavior,
});