第89页的代码还有更进一步的简化方法

var update_highlight = function (message_num) {
        var thumbs_up = $("#thumbs_up" + message_num);
        var thumbs_down = $("#thumbs_down" + message_num);
        var vote_value = $("#vote_value" + message_num).html();
        var hi = "highlighted";
        vote_value === "Up" ? thumbs_up.addClass(hi)
                                         : thumbs_up.removeClass(hi);
        vote_value === "Down" ? thumbs_down.addClass(hi)
                                              : thumbs_down.removeClass(hi);
};