I created a draggable carousel with momentum scrolling and mobile support using Vanilla JavaScript
Tags: javascript, tutorial, webdev, programming
Published: 2021-10-21 11:24:27

A few weeks ago I saw a really nice carousel on the Stripe blog. So I decided to replicate it and integrate it with WordPress. Here are my steps.

See a demo on my homepage here - https://getbutterfly.com/

## The WordPress Loop

I am getting the last 10 posts in the JavaScript category, I am setting up a counter and changing background colours based on this counter.

```
<?php
function whiskey_carousel() {
    $args = [
        'post_status' => 'publish',
        'post_type' => 'post',
        'posts_per_page' => 10,
        'category_name' => 'javascript'
    ];

    $featuredQuery = new WP_Query($args);

    $colours = [
        '#02bcf5', '#0073e6', '#003ab9', '#635bff', '#002c59', '#09cbcb',
        '#02bcf5', '#0073e6', '#003ab9', '#635bff', '#002c59', '#09cbcb',
    ];
    $i = 0;

    $data = '<div class="whiskey-cards">';

        if ($featuredQuery->have_posts()) {
            while ($featuredQuery->have_posts()) {
                $featuredQuery->the_post();

                $postID = get_the_ID();
                $excerpt = html_entity_decode(wp_trim_words(get_the_excerpt(), 32));

                $data .= '<div class="whiskey-card" style="background-color: ' . $colours[$i] . ';">
                    <h3><a href="' . get_permalink($postID) . '">' . get_the_title($postID) . '</a></h3>
                    <p class="whiskey-card--content">' . $excerpt . '</p>
                    <p class="whiskey-card--link"><a href="' . get_permalink($postID) . '">Learn more <svg class="HoverArrow" width="10" height="10" viewBox="0 0 10 10" aria-hidden="true"><g fill-rule="evenodd"><path class="HoverArrow__linePath" d="M0 5h7"></path><path class="HoverArrow__tipPath" d="M1 1l4 4-4 4"></path></g></svg></a></p>
                </div>';

                $i++;
            }
        }

    $data .= '</div>';

    return $data;
}

add_shortcode('whiskey-carousel', 'whiskey_carousel');
```

## The JavaScript Code

The JavaScript features momentum scrolling (mouse wheel) and (almost) native HTML dragging behaviour. The dragging is also available to mobile devices, as the content is overflowing horizontally.

```
document.addEventListener('DOMContentLoaded', () => {
    if (document.querySelector('.whiskey-cards')) {
        // Slider dragging
        const slider = document.querySelector('.whiskey-cards');
        let isDown = false;
        let startX;
        let scrollLeft;

        slider.addEventListener('mousedown', (e) => {
            isDown = true;
            slider.classList.add('active');
            startX = e.pageX - slider.offsetLeft;
            scrollLeft = slider.scrollLeft;
            cancelMomentumTracking();
        });

        slider.addEventListener('mouseleave', () => {
            isDown = false;
            slider.classList.remove('active');
        });

        slider.addEventListener('mouseup', () => {
            isDown = false;
            slider.classList.remove('active');
            beginMomentumTracking();
        });

        slider.addEventListener('mousemove', (e) => {
            if (!isDown) return;
            e.preventDefault();
            const x = e.pageX - slider.offsetLeft;
            const walk = (x - startX); //scroll-fast
            var prevScrollLeft = slider.scrollLeft;
            slider.scrollLeft = scrollLeft - walk;
            velX = slider.scrollLeft - prevScrollLeft;
        });

        // Momentum 
        var velX = 0;
        var momentumID;

        slider.addEventListener('wheel', (e) => {
            cancelMomentumTracking();
        });

        function beginMomentumTracking() {
            cancelMomentumTracking();
            momentumID = requestAnimationFrame(momentumLoop);
        }

        function cancelMomentumTracking() {
            cancelAnimationFrame(momentumID);
        }

        function momentumLoop() {
            slider.scrollLeft += velX * 2;
            velX *= 0.95;
            if (Math.abs(velX) > 0.5) {
                momentumID = requestAnimationFrame(momentumLoop);
            }
        }

        // Scroll
        const scrollContainer = document.querySelector(".whiskey-cards");

        scrollContainer.addEventListener("wheel", (evt) => {
            evt.preventDefault();

            window.requestAnimationFrame(() => {
                scrollContainer.scrollTo({ top: 0, left: scrollContainer.scrollLeft + (evt.deltaY * 2), behavior: "smooth" });
            });
        });
    }
});
```

## The CSS Style

And finally, there are lots of opinionated styles below, so make sure you get what you need.

```
.whiskey-cards {
    display: flex;
    flex-wrap: nowrap;
    overflow-x: scroll;
    -webkit-overflow-scrolling: touch;
    -ms-overflow-style: none;
    scrollbar-width: none;

    padding: 48px 48px 0 48px;

}
.whiskey-cards::-webkit-scrollbar {
    -webkit-appearance: none;
    width: 5px;
    height: 5px;
}
.whiskey-cards::-webkit-scrollbar-thumb {
    border-radius: 0;
    background-color: rgba(0, 0, 0, .5);
    background: linear-gradient(90deg, #02bcf5, #0073e6, #003ab9, #635bff);
    box-shadow: 0 0 1px rgba(255, 255, 255, .5);
    border-radius: 16px;
    opacity: .5;
}
.whiskey-cards:hover::-webkit-scrollbar-thumb {
    opacity: 1;
}

.whiskey-card {
    display: flex;
    flex-direction: column;
    min-width: 244px;
    flex-basis: 244px;
    border-radius: 16px;
    margin: 8px;
    padding: 16px;
    box-shadow: 0 -16px 24px rgb(0 0 0 / 5%);
    color: #ffffff;

    transition: all 150ms cubic-bezier(0.215,0.61,0.355,1);
}
.whiskey-card:hover {
    background-color: #0a2540 !important;
    transform: scale(1.04) translateY(-16px);
    box-shadow: 0 -16px 24px rgb(0 0 0 / 10%);
}
.whiskey-card h3 {
    padding-top: 0;
    line-height: 1.35;
}
.whiskey-card .whiskey-card--content {
    line-height: 1.5;
    font-size: 15px;
    font-weight: 300;
}
.whiskey-card .whiskey-card--link {
    line-height: 1.5;
    font-size: 15px;
    font-weight: 700;
    opacity: .7;
    margin: auto 0 0 0;
}
.whiskey-card h3 a,
.whiskey-card .whiskey-card--link a {
    color: #ffffff;
}
.whiskey-card .whiskey-card--link a svg {
    --arrowSpacing: 5px;
    --arrowHoverTransition: 150ms cubic-bezier(0.215,0.61,0.355,1);
    --arrowHoverOffset: translateX(3px);
    --arrowTipTransform: none;
    --arrowLineOpacity: 0;
    position: relative;
    top: 1px;
    margin-left: var(--arrowSpacing);
    stroke-width: 2px;
    fill: none;
    stroke: currentColor;
}
.HoverArrow__linePath {
    opacity: var(--arrowLineOpacity);
    transition: opacity var(--hoverTransition,var(--arrowHoverTransition));
}
.HoverArrow__tipPath {
    transform: var(--arrowTipTransform);
    transition: transform var(--hoverTransition,var(--arrowHoverTransition));
}
.whiskey-card:hover .HoverArrow__linePath {
    --arrowLineOpacity: 1;
}
.whiskey-card:hover .HoverArrow__tipPath {
    --arrowTipTransform: var(--arrowHoverOffset);
}
```

I wrote about this and other [JavaScript carousels and sliders here](https://getbutterfly.com/how-to-create-a-draggable-carousel-using-vanilla-javascript/).