MediaWiki:Common.js

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(function () {
    var sidebarId = 'mw-navigation';

    // Save the sidebar scroll position to URL parameter
    function saveSidebarScrollPosition() {
        var scrollPosition = document.getElementById(sidebarId).scrollTop;
        var newUrl = updateUrlParameter(window.location.href, 'sidebarScroll', scrollPosition);
        window.history.replaceState(null, '', newUrl);
    }

    // Restore the sidebar scroll position from URL parameter
    function restoreSidebarScrollPosition() {
        var scrollPosition = getUrlParameter('sidebarScroll');
        if (scrollPosition !== null) {
            document.getElementById(sidebarId).scrollTop = parseInt(scrollPosition);
        }
    }

    // Update URL parameter
    function updateUrlParameter(uri, key, value) {
        var re = new RegExp("([?&])" + key + "=.*?(&|$)", "i");
        var separator = uri.indexOf('?') !== -1 ? "&" : "?";
        if (uri.match(re)) {
            return uri.replace(re, '$1' + key + "=" + value + '$2');
        } else {
            return uri + separator + key + "=" + value;
        }
    }

    // Get URL parameter
    function getUrlParameter(name) {
        name = name.replace(/[\[]/, '\\[').replace(/[\]]/, '\\]');
        var regex = new RegExp('[\\?&]' + name + '=([^&#]*)');
        var results = regex.exec(location.search);
        return results === null ? null : decodeURIComponent(results[1].replace(/\+/g, ' '));
    }

    // Save the sidebar scroll position before navigating away
    window.addEventListener('beforeunload', saveSidebarScrollPosition);

    // Restore the sidebar scroll position on page load
    window.addEventListener('DOMContentLoaded', restoreSidebarScrollPosition);

    // Save the sidebar scroll position when clicking on sidebar links
    document.querySelectorAll('#' + sidebarId + ' a').forEach(function (link) {
        link.addEventListener('click', function (event) {
            saveSidebarScrollPosition();
        });
    });
})();