Jquery Uncaught TypeError: Cannot read property 'replace' of undefined

Question

Anyone can tell me why i am getting this error:

Uncaught TypeError: Cannot read property 'replace' of undefined

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();

Answer 1

I believe that this error is caused by one of two scenarios, based on the given information above:

1. $('#NewPostBody) is not being found in the DOM

2. $('#NewPostBody) is being found but has no class attribute.

This can be solved using the following method:

var pid = ($('#NewPostBody').length && $('#NewPostBody').attr('class')) 
    ? $('#NewPostBody').attr('class') 
    : "";

The ternary operator along with truthy/falsy logic should result in either the class being returned or an empty string. Either way, pid.replace('post-t', '') can safely be called without resulting in an error.