mp-history-deeplinking.js

function urlFromHash() {
    if (location.hash.substr(0, 2) != '#!') {
        return null;
    }
    // why not location.hash? => http://stackoverflow.com/q/4835784/298479
    return location.href.split('#')[1].substr(1);
}

$('#gallery').magnificPopup({
    type: 'image',
    delegate: 'a[rel="photo"]',
    key: 'photos',
    gallery: {
        enabled: true,
        preload: [0, 2]
    },
    callbacks: {
        close: function () {
            location.hash = '';
        },
        change: function (item) {
            location.hash = '#!' + item.el.attr('href');
        }
    }
});

var hashUrl = urlFromHash();
if (hashUrl) {
    $pm.find('a[href="' + hashUrl + '"]').trigger('click');
}

$(window).on('hashchange', function () {
    var mp = $.magnificPopup.instance;
    if (!mp) {
        // this check is not needed in this example, but in some cases you might delay everything before
        // this event e.g. until something else finished loading - in that case hashchange might trigger before
        return;
    }

    var url = urlFromHash();
    if (!url && mp.isOpen) {
        // no url => close popup
        mp.close();
    } else if (url) {
        if (!mp.isOpen) {
            // not open => simply click the matching link
            gallery.find('a[href="' + url + '"]').trigger('click');
        } else if (!mp.currItem || mp.currItem.el.attr('href') != url) {
            // open => only update if necessary
            var index = null;
            $.each(mp.items, function (i, item) {
                var jqItem = item.parsed ? item.el : $(item);
                if (jqItem.attr('href') == url) {
                    index = i;
                    return false;
                }
            });
            if (index !== null) {
                mp.goTo(index);
            }
        }
    }
});