JSFiddle - React, Tailwind, and code Playground

by Steven Senkus

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/waypoints/4.0.0/jquery.waypoints.js"></script>
<div class="container">
    <div id="list_container">
        <ul>
            <li>
                 <h3>Zero</h3>

                <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum</p>
            </li>
            <li>
                 <h3>One</h3>

                <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum</p>
            </li>
            <li>
                 <h3>Two</h3>

                <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum</p>
            </li>
            <li>
                 <h3>Three</h3>

                <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit,...

CSS

body {
    width: 100%;
    text-align: center;
}
#list_container {
    width: 500px;
    height: 200px;
    overflow: scroll;
    background-color: #007;
    color: #fff;
    text-align: left;
    margin: 50px auto 10px;
}
#list_container ul {
    list-style-type: none;
    padding: 0;
    margin: 0 0 0px;
}
#list_container ul li {
    border: 1px solid #000;
}
#output {
    border: 1px solid #000;
}

JavaScript

(function ($) {
    var $container = $('#list_container')
    var colors = ['#f00', '#f70', '#dd0', '#0d0']

    $container.on('scroll', function (e) {

        $(this).find('ul li').each(function (index, el) {
         //   console.log(el, index);
          //  console.log(arguments);
            var isVisible = isScrolledIntoView($(el));
            if (isVisible) {
                $container.css({
                    'background-color': colors[index]
                });
                console.log(isVisible, index, $(el).find('h3').text());
                var html = $(el).html();
                $('#output').find('ul').empty().html(html)
            }
        });

    });

    $('#list_container').on('scroll', function (e) {
        var html = $(this).find('ul li:visible').html();
        $('#output').find('ul').html(html)
    });


    function isScrolledIntoView(elem) {
        var $elem = elem
        var $window = $(window);
        var docViewTop = $window.scrollTop();
        var docViewBottom = docViewTop + $window.height();
       // console.log('offset', $elem.offset());
        var elemTop = $elem.offset() && $elem.offset().top;
        var elemBottom = elemTop + $elem.height();
var bottom = ((elemBottom <= docViewBottom)) ;
              var top = (elemTop >= docViewTop);
        return bottom;
    }


})(jQuery)