src/js/theme/navigation.js
function getChapterHash($chapter) {
    var $link = $chapter.children('a'),
        hash = $link.attr('href').split('#')[1];

    if (hash) hash = '#'+hash;
    return (!!hash)? hash : '';
}
function getChapterHash($chapter) {
    var $link = $chapter.children('a'),
        hash = $link.attr('href').split('#')[1];

    if (hash) hash = '#'+hash;
    return (!!hash)? hash : '';
}
Return the hash of link for a chapter