JQuery检测滚动期间div是否可见

Question

我在项目中使用jQuery Mouse Wheel来操纵特定div上的滚动。

var viewWidth = $(window).width();
var temoignagesWidth = $('#temoignages .container-fluid').width();
var maxScrollTemoignages = temoignagesWidth - viewWidth;
var scrollVal = 0;
var temoignagesDiv = getTemoignagesDiv();

$(window).mousewheel(function(event){
    if (temoignagesDiv.top <= $(window).scrollTop() + navbarHeight && $(window).scrollTop() + $(window).height() < temoignagesDiv.bot){
        scrollVal += Math.round(event.deltaY * event.deltaFactor);

        var scrollUp = function(scrollVal){
            return scrollVal <= 0;
        };
        var scrollDown = function(scrollVal){
            return Math.abs(scrollVal) <= maxScrollTemoignages;
        };

        var condition = null;
        if (event.deltaY > 0){
            scrollVal = scrollUp(scrollVal) ? scrollVal : 0;
            condition = scrollUp(scrollVal);
        } else{
            scrollVal = scrollDown(scrollVal) ? scrollVal : maxScrollTemoignages * -1;
            condition = scrollDown(scrollVal);
    }

        if (condition){
            if (event.deltaY > 0 && scrollVal < 0){
                event.preventDefault();
            } else if (event.deltaY < 0 && Math.abs(scrollVal) < maxScrollTemoignages ){
                event.preventDefault();
            }

            $('#temoignages .row').css({
                "-webkit-transform":"translate(" + scrollVal + "px)", 
                "-ms-transform":"translate(" + scrollVal + "px)",  
                "transform":"translate(" + scrollVal + "px)"
            });
        }
    }
});

它运行良好但有时当我滚动条件时temoignagesDiv.top <= $(window).scrollTop() + navbarHeight && $(window).scrollTop() + $(window).height() < temoignagesDiv.bot未验证，因此代码不会被执行。有什么想法改进吗？ ：■