弹层禁止页面底部滚动

let bodyEl = document.body
let top = 0
function stopBodyScroll (isFixed) {
     if (isFixed) {
         top = window.scrollY
         bodyEl.style.position = 'fixed'
         bodyEl.style.top = -top + 'px'
     } else {
         bodyEl.style.position = ''
         bodyEl.style.top = ''
         window.scrollTo(0, top) // 回到原先的top
     }
}