找不到jQuery AJAX网址

I am trying to have a form add a comment to the database with ajax. The problem I am having is that ajax cannot find the url because of how my current url is structured

url.com/thread/id

I am trying to have the ajax request sent to

url.com/ajax_comment

If I enter the whole URL it works correctly. However I need to avoid doing so as this script will be installable on multiple domains. So how can I accomplish this without hard coding the url in?

Is there a structure in javascript, similar to PHP where you can do include('./folder/file.php'); or there is another method to accomplish this?

Why not to use relative URLs?

$.ajax({
    url: "/ajax_comment",
    ...
});

A relative url will work. This will retrieve the current domain and append your page string to it:

window.location.protocol+"//"+window.location.hostname+"/ajax_comment"