jQuery滚动条滚动显示手机菜单

右下角菜单html代码

<div id="cd-nav">
    <a href="javascript:void(0)" class="cd-nav-trigger">Menu<span></span></a>

    <nav id="cd-main-nav">
        <ul>
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        </ul>
    </nav>
</div>

滚动时判断是否显示右下角菜单

$(window).scroll(function() {
    checkMenu();
});

function checkMenu() {
    if ($(window).scrollTop() > offset && !navigationContainer.hasClass('is-fixed')) {
        navigationContainer.addClass('is-fixed').find('.cd-nav-trigger').one('webkitAnimationEnd oanimationend msAnimationEnd animationend', function() {
            mainNavigation.addClass('has-transitions');
        });
    } else if ($(window).scrollTop() <= offset) {
        //check if the menu is open when scrolling up
        if (mainNavigation.hasClass('is-visible') && !$('html').hasClass('no-csstransitions')) {
            //close the menu with animation
            mainNavigation.addClass('is-hidden').one('webkitTransitionEnd otransitionend oTransitionEnd msTransitionEnd transitionend', function() {
                //wait for the menu to be closed and do the rest
                mainNavigation.removeClass('is-visible is-hidden has-transitions');
                navigationContainer.removeClass('is-fixed');
                $('.cd-nav-trigger').removeClass('menu-is-open');
            });
            //check if the menu is open when scrolling up - fallback if transitions are not supported
        } else if (mainNavigation.hasClass('is-visible') && $('html').hasClass('no-csstransitions')) {
            mainNavigation.removeClass('is-visible has-transitions');
            navigationContainer.removeClass('is-fixed');
            $('.cd-nav-trigger').removeClass('menu-is-open');
            //scrolling up with menu closed
        } else {
            navigationContainer.removeClass('is-fixed');
            mainNavigation.removeClass('has-transitions');
        }
    }
}