mounted(){
window.addEventListener('scroll',this.handleScroll)
},
methods:{
handleScroll(){
let scrollTop = window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop // 滚动条偏移量
let offsetTop = document.querySelector('.big-b').offsetTop; //绑定节点的偏移量
this.scrollTop=scrollTop
}
}