beforeRouteLeave(to, from, next){
  let position = window.scrollY()
  this.$store.commit('SAVE_POSITION', position) //离开路由时把位置存起来
}

在页面中取值

mounted () {
  this.$nextTick(function(){
    let position = this.$store.state.position //返回页面取出来
    window.scroll(0, position)
  }) 
}