For Removing Class and Adding Class based on the scroll position

help.js

<div id="menuBar" class="nav-menu"></div>
<div style="margin-bottom: 999em;"></div>

<script type="text/javascript">
$(document).ready(function(){

    $(window).on('scroll', function () {  
        var $body = $('body');
        var $target = $('#menuBar');
        if ($body.scrollTop() > 100 && $target.hasClass('nav-menu')){
                $target.removeClass("nav-menu");    
        }
        else if( $body.scrollTop() <= 100 && !$target.hasClass('nav-menu') ){ 
            $target.addClass('nav-menu');
        }

    });

});
</script>