$(document).ready(function(){
  $("#chk").click(function(){
	var username = $("#username").val();
	var ajax_load = "<img src='../images/ajax-loader.gif' alt='loading...' />";  
   $.ajax({
    type : "POST",
    url : "checkUser.php",
    data : "user=" + username,
    success : function(html){
     $("#xresult").html(html);
    }
   });
  });
 });