index.html

<div class="container">
    <div class="row">
        <div class="col-full col-xs-12 col-sm-12 col-md-12 col-lg-12">
            <div class="gallery | js-gallery">
                <figure class="gallery__item | js-gallery-item"><a href="http://lorempixel.com/1200/800/sports/1" data-size="1200x800"><img src="http://lorempixel.com/1200/800/sports/1" /></a></figure>
                <figure class="gallery__item | js-gallery-item"><a href="http://lorempixel.com/1200/800/sports/2" data-size="1200x800"><img src="http://lorempixel.com/1200/800/sports/2" /></a></figure>
            </div><!-- /.gallery -->

            <div class="gallery gallery--nav | js-gallery-nav">
                <div class="gallery__item gallery__item--nav" style="background-image: url('http://lorempixel.com/300/200/sports/1');"></div><!-- /.gallery__item -->
                <div class="gallery__item gallery__item--nav" style="background-image: url('http://lorempixel.com/300/200/sports/2');"></div><!-- /.gallery__item -->
            </div><!-- /.gallery -->
        </div><!-- /.col-full col-xs-12 col-sm-12 col-md-12 col-lg-12 -->
    </div><!-- /.row -->
</div><!-- /.container -->

<div class="pswp" tabindex="-1" role="dialog" aria-hidden="true">
    <div class="pswp__bg"></div>
    <div class="pswp__scroll-wrap">
        <div class="pswp__container">
            <div class="pswp__item"></div>
            <div class="pswp__item"></div>
            <div class="pswp__item"></div>
        </div>
        <div class="pswp__ui pswp__ui--hidden">
            <div class="pswp__top-bar">
                <div class="pswp__counter"></div>
                <button class="pswp__button pswp__button--close" title="Close (Esc)"></button>
                <button class="pswp__button pswp__button--share" title="Share"></button>
                <button class="pswp__button pswp__button--fs" title="Toggle fullscreen"></button>
                <button class="pswp__button pswp__button--zoom" title="Zoom in/out"></button>
                <div class="pswp__preloader">
                    <div class="pswp__preloader__icn">
                      <div class="pswp__preloader__cut">
                        <div class="pswp__preloader__donut"></div>
                      </div>
                    </div>
                </div>
            </div>
            <div class="pswp__share-modal pswp__share-modal--hidden pswp__single-tap">
                <div class="pswp__share-tooltip"></div>
            </div>
            <button class="pswp__button pswp__button--arrow--left" title="Previous (arrow left)">
            </button>
            <button class="pswp__button pswp__button--arrow--right" title="Next (arrow right)">
            </button>
            <div class="pswp__caption">
                <div class="pswp__caption__center"></div>
            </div>
        </div>
    </div>
</div>

Main.js

$('.js-gallery').on('init', function (slick) {
    photoswipe();
});

// Slick
$('.js-gallery').slick({
    slidesToShow: 1,
    slidesToScroll: 1,
    arrows: false,
    draggable: false,
    fade: true,
    asNavFor: '.js-gallery-nav',
});

$('.js-gallery-nav').slick({
    slidesToShow: 5,
    slidesToScroll: 1,
    centerMode: true,
    arrows: false,
    asNavFor: '.js-gallery',
    focusOnSelect: true
});

Package.json

"dependencies": {
    "photoswipe": "^4.1.1",
    "slick-carousel": "^1.6.0"
}

Photoswipe.js

function photoswipe() {
    var initPhotoSwipeFromDOM = function(gallerySelector) {

        // parse slide data (url, title, size ...) from DOM elements
        // (children of gallerySelector)
        var parseThumbnailElements = function(el) {
            var thumbElements = el.childNodes,
                numNodes = thumbElements.length,
                items = [],
                figureEl,
                linkEl,
                size,
                item;

            for(var i = 0; i < numNodes; i++) {

                figureEl = thumbElements[i]; // <figure> element

                // include only element nodes
                if(figureEl.nodeType !== 1) {
                    continue;
                }

                linkEl = figureEl.children[0]; // <a> element

                size = linkEl.getAttribute('data-size').split('x');

                // create slide object
                item = {
                    src: linkEl.getAttribute('href'),
                    w: parseInt(size[0], 10),
                    h: parseInt(size[1], 10)
                };



                if(figureEl.children.length > 1) {
                    // <figcaption> content
                    item.title = figureEl.children[1].innerHTML;
                }

                if(linkEl.children.length > 0) {
                    // <img> thumbnail element, retrieving thumbnail url
                    item.msrc = linkEl.children[0].getAttribute('src');
                }

                item.el = figureEl; // save link to element for getThumbBoundsFn
                items.push(item);
            }

            return items;
        };

        // find nearest parent element
        var closest = function closest(el, fn) {
            return el && ( fn(el) ? el : closest(el.parentNode, fn) );
        };

        // triggers when user clicks on thumbnail
        var onThumbnailsClick = function(e) {
            e = e || window.event;
            e.preventDefault ? e.preventDefault() : e.returnValue = false;

            var eTarget = e.target || e.srcElement;

            // find root element of slide
            var clickedListItem = closest(eTarget, function(el) {
                return (el.tagName && el.tagName.toUpperCase() === 'FIGURE');
            });

            if(!clickedListItem) {
                return;
            }

            // find index of clicked item by looping through all child nodes
            // alternatively, you may define index via data- attribute
            var clickedGallery = clickedListItem.parentNode,
                childNodes = clickedListItem.parentNode.childNodes,
                numChildNodes = childNodes.length,
                nodeIndex = 0,
                index;

            for (var i = 0; i < numChildNodes; i++) {
                if(childNodes[i].nodeType !== 1) {
                    continue;
                }

                if(childNodes[i] === clickedListItem) {
                    index = nodeIndex;
                    break;
                }
                nodeIndex++;
            }



            if(index >= 0) {
                // open PhotoSwipe if valid index found
                openPhotoSwipe( index, clickedGallery );
            }
            return false;
        };

        // parse picture index and gallery index from URL (#&pid=1&gid=2)
        var photoswipeParseHash = function() {
            var hash = window.location.hash.substring(1),
            params = {};

            if(hash.length < 5) {
                return params;
            }

            var vars = hash.split('&');
            for (var i = 0; i < vars.length; i++) {
                if(!vars[i]) {
                    continue;
                }
                var pair = vars[i].split('=');
                if(pair.length < 2) {
                    continue;
                }
                params[pair[0]] = pair[1];
            }

            if(params.gid) {
                params.gid = parseInt(params.gid, 10);
            }

            return params;
        };

        var openPhotoSwipe = function(index, galleryElement, disableAnimation, fromURL) {
            var pswpElement = document.querySelectorAll('.pswp')[0],
                gallery,
                options,
                items;

            items = parseThumbnailElements(galleryElement);

            // define options (if needed)
            options = {

                // define gallery index (for URL)
                galleryUID: galleryElement.getAttribute('data-pswp-uid'),

                getThumbBoundsFn: function(index) {
                    // See Options -> getThumbBoundsFn section of documentation for more info
                    var thumbnail = items[index].el.getElementsByTagName('img')[0], // find thumbnail
                        pageYScroll = window.pageYOffset || document.documentElement.scrollTop,
                        rect = thumbnail.getBoundingClientRect();

                    return {x:rect.left, y:rect.top + pageYScroll, w:rect.width};
                }

            };

            // PhotoSwipe opened from URL
            if(fromURL) {
                if(options.galleryPIDs) {
                    // parse real index when custom PIDs are used
                    // http://photoswipe.com/documentation/faq.html#custom-pid-in-url
                    for(var j = 0; j < items.length; j++) {
                        if(items[j].pid == index) {
                            options.index = j;
                            break;
                        }
                    }
                } else {
                    // in URL indexes start from 1
                    options.index = parseInt(index, 10) - 1;
                }
            } else {
                options.index = parseInt(index, 10);
            }

            // exit if index not found
            if( isNaN(options.index) ) {
                return;
            }

            if(disableAnimation) {
                options.showAnimationDuration = 0;
            }

            // Pass data to PhotoSwipe and initialize it
            gallery = new PhotoSwipe( pswpElement, PhotoSwipeUI_Default, items, options);
            gallery.init();
        };

        // loop through all gallery elements and bind events
        var galleryElements = document.querySelectorAll( gallerySelector );

        for(var i = 0, l = galleryElements.length; i < l; i++) {
            galleryElements[i].setAttribute('data-pswp-uid', i+1);
            galleryElements[i].onclick = onThumbnailsClick;
        }

        // Parse URL and open gallery if it contains #&pid=3&gid=1
        var hashData = photoswipeParseHash();
        if(hashData.pid && hashData.gid) {
            openPhotoSwipe( hashData.pid ,  galleryElements[ hashData.gid - 1 ], true, true );
        }
    };

    // execute above function
    initPhotoSwipeFromDOM('.js-gallery');
}