gistfile1.js

this.$suggest = $('div.p-suggest');

var navigateSuggestions = function(direction) {
    var $active = this.$suggest.find('.active'),
        listLenght = this.$suggest.find('ul > li').length,
        index;

    if ($active.length > 0) {
        index = (direction === 38) ? $active.index() - 1 : $active.index() + 1;
        console.log(index, listLenght);
        if (index === listLenght) {
            index = 0;
        }
        $item = this.$suggest.find('ul > li:eq(' + index + ')');
        if ($item.length > 0) {
            $active.removeClass('active');
            $item.addClass('active');
        }
    } else {
        this.$suggest.find('ul > li:first-child').addClass('active');
    }
};

(function($) {
    $('input.p-search_input').on('keyup', function(event) {
        event.preventDefault();
        if (event.keyCode === 38 || event.keyCode === 40) {
            navigateSuggestions(event.keyCode);
        }
    });
}(jQuery));