Custom progress bar for reading progression

Display a progress bar moving according to where you are in the article reading. Clickable progress bar to jump to the percentage. Bonus: sticky progress bar.

by Paf_Sebastien

HTML

<div class="progress-container">
    <div class="progress">
        <div class="bar"></div>
        <div class="marker"></div>
        <div class="tooltip">25%</div>
    </div>
</div>
<article>
    <p><a href="https://twitter.com/Semaho_" target="_blank">SĂ©bastien</a> @ <a href="http://pafdesign.be/" target="_target">Paf!</a></p>
    <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>
    <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. 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>
    <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...

CSS

* {
    box-sizing: border-box;
}

body {
    padding-top: 100px;
    background-color: #ebebeb;
}

.progress-container {
    position: absolute;
    top: 50px; left: 0;
    width: 100%;
}
.progress-container.sticky {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    padding: 10px 0;
    background-color: #ebebeb;
}

.progress {
    position: relative;
    width: 90%;
    background: #fff;
    margin: 0 auto;
    /*overflow: hidden;*/
    box-shadow: 1px 1px 0 #CCC;
    cursor: pointer;
}

.bar {
    height: 10px;
    background-color: #00BABA;
    width: 0%;
    transition: .2s;
}

.marker {
    width: 2px; height: 10px;
    background-color: #00BABA;
    position: absolute;
    left: 0; top: 0;
}

.tooltip {
    display: none;
    position: absolute;
    top: 30px; left: 0;
    background-color: #444;
    color: #fff;
    padding: 6px 10px;
    border-radius: 2px;
}

article {
    width: 90%;
    margin: 0 auto;
    padding: 50px;
    background-color: #fff;
    margin-bottom: 100px;
}
article p {
    line-height: 1.4em;
}

JavaScript

$(function()
{
    // Declare DOM elements.
    $window   = $(window);
    $document = $(document);
    $prog_cont= $('.progress-container');
    $progress = $('.progress');
    $bar      = $('.bar');
    $marker   = $('.marker');
    $tooltip   = $('.tooltip');
    $article  = $('article');
    
    articleHeight = $article.height();
    
    progressInitialOffset = $prog_cont.offset().top;
    offsetBeforeSticky    = 10; // Distance between element and window top border before beeing sticky.
    
    // Init event detection.
    initOnScroll();
    initProgressOnClick();
    initProgressOnHover();
    
    // Simulate scroll to update progress bar on "document ready".
    $document.scroll();
});


// Detect scroll and update progress bar.
function initOnScroll()
{
    $document.on('scroll', function()
    {
        updateProgressPosition();
        
        var articleScrollTop  = $article.offset().top - $window.scrollTop();
        var lowestVisiblePart = $window.height() - articleScrollTop;
        var readingPct        = Math.round( lowestVisiblePart / articleHeight * 100 );
        updateBar( readingPct );
    });
}


function updateBar(width)
{
    if (width > 100) width = 100;
    $bar.css('width', width+'%');
}


// Detect click and ONLY scroll to position, the 'scroll' event will update the bar.
function initProgressOnClick()
{
    $progress.click(function(e)
    {
        var clickRelativePos = e.pageX - $progress.offset().left;
        var clickPosPct      = Math.round( clickRelativePos / $progress.width() * 100 );
        
        var wantedLowestVisiblePart = articleHeight * (clickPosPct/100);
        articleScrollPos = wantedLowestVisiblePart + $article.offset().top - $window.height();
        $('body').animate({scrollTop: articleScrollPos}, 200);
    });
}


function initProgressOnHover()
{
    $progress.on('mousemove', function(e) {
        // Mouse enter.
        var mouseRelativePos = e.pageX - $progress.offset().left;
        var mousePosPct  ...