绑定在window上 addEventListener 事件需要 第三个参数设置为true，不然事件不起作用

 mounted() {
    window.addEventListener('scroll',this.handleScroll,true)
  }
 methods: {
  handleScroll(){
      let scrollTop = document.body.scrollTop || document.documentElement.scrollTop;
      console.log(scrollTop);
    }
}

绑定到元素上

mounted() {
    document.querySelector("#wrap").addEventListener('scroll',this.handleScroll)
 }
methods: {
  handleScroll(){
      let scrollTop = document.querySelector("#wrap").scrollTop;
      console.log(scrollTop);
    }
}