title: Cannot put checking in ajax
body: <p>I have a bootbox dialog with a button. There is a problem with the 1st ajax function in there.
  I would like to check whether the value returned from model and controller is 0 or 1 and stop the callback function from posting data to database if the value it returns is 1. However, once I put this check , it doesn't work before putting the first ajax function with the check, everything works perfectly. Now, I cannot even save any data to the database.</p>
  
  <pre><code>buttons: {
      success: {
          label: "Save",
          className: "btn-success",
          callback: function() {
              console.log('save');
              console.log($('#re_confirm')[0].checked);
              ...
              ...
              ...
  
              var check;
                  $.ajax({
                  url: "&lt;?php echo base_url(); ?&gt;index.php/home/check_occupied",
                  type: "post", // To protect sensitive data
                  data: {
                          "table_id" : valueid2,
                          "session_id" : table_column_14,
                      //and any other variables you want to pass via POST
                        },
                  success:function(response){
                  // Handle the response object
                      check=response;
                  },
              });
  
             if(check!=0)
              return;
  
             $.ajax({
                  url : "&lt;?php echo base_url(); ?&gt;index.php/home/update_booking",
                  type: "post",
                  data: {
                     "table_id" : $('#idtable').val(),
                  },
                  success: function(response){
                  ...
                  }
              });
          }
      },
  ...
  ,
  ...
  }
  });
  </code></pre>