windowScroll，监听页面滚动距离

mounted() {
    window.addEventListener("scroll", this.windowScroll);//监听页面滚动
},
methods: {
    //页面滚动,导航切换显示
    windowScroll() {
        let scrollTop = window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop;
        let dom = document.querySelector(".dom").offsetTop;
    },
},
destroyed() {
    window.removeEventListener("scroll", this.windowScroll);//销毁滚动事件
}