[Dremlin]

function showLoader() 
{
 $('#loadingDiv').show();
};

function hideLoader() 
{
 $('#loadingDiv').hide();
};
function doRequest() 
{
 showLoader();
  $.ajax({
  type: "POST",
  url: "youscript.xxx",
  success: function (result) 
  {
   if (result == 'True') {
   alert("Request is done!");
  } 
   else 
  {
   alert("Request is fail!");
   };
},

complete: function () 
{
  hideLoader();
}
});
};

Логика примерно такая, вот.