如何判断一个元素是否因为上下滚动而被隐藏

function isScrollShow(elem){  //判断元素是否因为滚动界面不可见了，认为只剩1/2的高度就不可见了
        var bounds = elem.getBoundingClientRect();
        var elemHeight = bounds.bottom-bounds.top;
        var show = true;
        var pBounds = elem.parentElement.parentElement.getBoundingClientRect(); //这里需要根据结构重新写
        console.log(pBounds.top ,bounds.top ,pBounds.bottom,bounds.bottom)
        if(pBounds.top - 1/2 * elemHeight > bounds.top ||  pBounds.bottom  + 1/2 * elemHeight <bounds.bottom ){
            show = false
        }
        return {top:bounds.top,height:elemHeight,show:show };

    }