Activate CSS3 animation when the content scrolls into view

Question

I have a bar chart that animates with CSS3 and the animation currently activates as the page loads.

The problem I have is that the given bar chart is placed off screen due to lots of content before it so by the time a user scrolls down to it, the animation has already finished.

I was looking for ways either through CSS3 or jQuery to only activate the CSS3 animation on the bar chart when the viewer sees the chart.

<div>lots of content here, it fills the height of the screen and then some</div>
<div>animating bar chat here</div>

If you scroll down really fast right after page load, you can see it animating.

Here is a jsfiddle of my code. Also, I don't know if this matters, but I have several instances of this bar chart on the page.

I have come across a jQuery plug-in called waypoint but I had absolutely no luck getting it to work.

Answer 1

Capture scroll events

This requires using JavaScript or jQuery to capture scroll events, checking each time a scroll event fires to see if the element is in view.

Once the element is in view, start the animation. In the code below, this is done by adding a "start" class to the element, that triggers the animation.

Updated demo

HTML

<div class="bar">
    <div class="level eighty">80%</div>
</div>

CSS

.eighty.start {
    width: 0px;
    background: #aae0aa;
    -webkit-animation: eighty 2s ease-out forwards;
       -moz-animation: eighty 2s ease-out forwards;
        -ms-animation: eighty 2s ease-out forwards;
         -o-animation: eighty 2s ease-out forwards;
            animation: eighty 2s ease-out forwards;
}

jQuery

function isElementInViewport(elem) {
    var $elem = $(elem);

    // Get the scroll position of the page.
    var scrollElem = ((navigator.userAgent.toLowerCase().indexOf('webkit') != -1) ? 'body' : 'html');
    var viewportTop = $(scrollElem).scrollTop();
    var viewportBottom = viewportTop + $(window).height();

    // Get the position of the element on the page.
    var elemTop = Math.round( $elem.offset().top );
    var elemBottom = elemTop + $elem.height();

    return ((elemTop < viewportBottom) && (elemBottom > viewportTop));
}

// Check if it's time to start the animation.
function checkAnimation() {
    var $elem = $('.bar .level');

    // If the animation has already been started
    if ($elem.hasClass('start')) return;

    if (isElementInViewport($elem)) {
        // Start the animation
        $elem.addClass('start');
    }
}

// Capture scroll events
$(window).scroll(function(){
    checkAnimation();
});