JSFiddle - React, Tailwind, and code Playground

by adamschwartz

HTML

<div id="scrollbox">
    <div id="box"></div>
    <div id="heightbox"></div>
    <div id="output"></div>
</div>

CSS

</style>
<meta name="viewport" content="width=device-width, initial-scale=1">

<style>
html, body {
    overflow: hidden;
    height: 100%;
    width: 100%;
}

body {
    margin: 0
}

#box {
    background: #000;
    height: 50px;
    width: 50px;
    position: fixed;
    top: -25px;
    bottom: 0;
    -webkit-transform: translate3d(0, 0, 0)
}

#heightbox {
    display: block;
    height: 3000px;
    width: 100%;
    background: -webkit-linear-gradient(#fff, #ccc);
    background-size: 100% 50px
}

output {
    position: fixed;
    margin: auto;
    display: inline-block;
    white-space: nowrap;
    padding: 20px;
    top: 0;
    bottom: 0;
    left: 100px;
    right: 100px;
    height: 30px;
    font-size: 30px;
    line-height: 30px;
    max-width: 500px;
    background: #000;
    color: #fff;
    text-align: center;
}

#scrollbox {
    overflow: auto;
    height: 100%;
    width: 100%;
    -webkit-overflow-scrolling: touch;
}

JavaScript

var reposition, interval, timeout, height;

reposition = function() {
    var scrollTop, windowHeight, position;
    
    scrollTop = scrollbox.scrollTop;
    windowHeight = window.innerHeight;
    scrollHeight = heightbox.clientHeight;
    
    console.log(scrollTop, windowHeight, scrollHeight);
    
    position = scrollTop * windowHeight / (scrollHeight - windowHeight);
    position = Math.floor(position);
    
    box.style.webkitTransform = 'translate3d(0, ' + position + 'px, 0)';
    output.innerHTML = position;
};

window.addEventListener('scroll', reposition);
scrollbox.addEventListener('scroll', reposition);
window.addEventListener('touchmove', reposition);
scrollbox.addEventListener('touchmove', reposition);

document.body.addEventListener('touchstart', function(e){
    clearTimeout(timeout);
    interval = setInterval(reposition);
});

document.body.addEventListener('touchend', function(e){
    timeout = setTimeout(function(){
        clearInterval(interval);
    }, 5000);
});