任何人都可以告诉我为什么我收到此错误：

未捕获的TypeError：无法读取未定义的属性’replace’

function checkNewPost(x) {
        var pid = $('#NewPostbody').attr('class');
        if(pid === 'post-t') {
            setTimeout(checkNewPost,PHP echo $p_id; ?>);
        } else {
            $.ajax({
                type: "POST",url: "/html_postReply.PHP",data: "pid="+pid.replace('post-t','')+"&type=1",success: function(html) {
                    if(html) {
                        $('.tekin').append(html);
                        jQuery("span.timeago").timeago();
                        $(".tekin").scrollTop($(".tekin")[0].scrollHeight);
                    }
                    if(!x) {
                        setTimeout(checkNewPost,PHP echo $p_id; ?>);
                    }
               }
            });
        }
    }
    checkNewPost();