focusable.js

/**
 * Add `:focusable` selector. (From jQuery UI)
 */
$.extend($.expr[':'], {
  focusable: function(element) {
    var hasTabIndex = $.attr(element, 'tabindex') != null;
    var nodeName = element.nodeName.toLowerCase();
    return (/^input|textarea|select|button$/.test(nodeName)
          ? !element.disabled
          : ('a' === nodeName
            ? element.href || hasTabIndex
            : hasTabIndex)
        ) && $(element).is(':visible') && visible($(element));
  }
});

// IE8 only
// IE8 doesn't resolve inherit to visible/hidden for computed values.
function visible(element) {
  var visibility = element.css('visibility');
  while (visibility === 'inherit') {
    element = element.parent();
    visibility = element.css('visibility');
  }
  return visibility !== 'hidden';
}