how to send multiple data with $.ajax() jquery

Question

i am trying to send multiple data using j query $.ajax method to my php script but i can pass only single data when i concatenate multiple data i get undefined index error i

Answer 1

var CommentData= "u_id=" + $(this).attr("u_id") + "&post_id=" + $(this).attr("p_id") + "&comment=" + $(this).val();