1. 添加属性screenHeight 和 timer。
screenHeight: window.innerHeight
timer: '' // window.onresize函数频繁调用时，页面抖动较大，设定间隔
2. 在mounted 钩子函数中监听onresize事件
let that = this
window.onresize = () => {
if (!that.timer) {
that.timer = true
setTimeout(() => {
that.timer = false
that.screenHeight = window.innerHeight
}, 600)
}
}
3. h5 新单位 vh,vw