mclibrary keyboard user dropdown menu support

/**
 * mclibrary keyboard user dropdown menu support
 */

// Add toggle button
jQuery('#main-menu > li > a').after('<button aria-expanded="false" class="wcag21-toggle"><span aria-hidden="true">&#9661;</span><span class="sr-only">Toggle sub menu</span></button>');
jQuery('.nav-dropdown').attr('tabindex','0').attr('aria-label','sub menu wrapper');

// Maintain aria-expanded attributes and show/hide sub menus
jQuery('.wcag21-toggle').bind('click', function (e) {
    var expandedState = jQuery(this).attr('aria-expanded');
    var id_of_sub = '#' + jQuery(this).parent().attr('class').split(" ").pop();

    if (expandedState == 'true') {
        jQuery(this).attr('aria-expanded', 'false');
        jQuery(id_of_sub).css('display','none');
    }
    else {
        jQuery(this).attr('aria-expanded', 'true');
        jQuery(id_of_sub).css('display','block');
        jQuery(id_of_sub).focus();
    }
    return false
});

// When sub menu has focus and user shift+tab backwards, send focus to it's triggering button
jQuery('.nav-dropdown').on('keydown', function(event) {
    if (event.shiftKey && event.keyCode == 9) {
        var this_subs_toggle_class = '.' + jQuery(this).attr('id');
        jQuery(this_subs_toggle_class).find('> button.wcag21-toggle').focus();
    }
    return false
});

// Hide menu on escape key
document.addEventListener('keydown', function(event) {
    if (event.key === "Escape") { // Escape key
        jQuery('.wcag21-toggle').attr('aria-expanded', 'false');
        jQuery(".nav-dropdown").css('display','none');
    }
    return false
});

// Maintain aria-expanded on hover
jQuery("#main-menu > li").bind('mouseenter', function () {
    jQuery(this).find('> button').attr('aria-expanded', 'true');
    return false
});
jQuery("#main-menu > li").bind('mouseleave', function () {
    jQuery(this).find('> button').attr('aria-expanded', 'false');
    return false
});