Solution 1:

There are a couple of ways. My preferred way is to attach a function to the ajaxStart/Stop events on the element itself.

$('#loadingDiv')
    .hide()  // Hide it initially
    .ajaxStart(function() {
        $(this).show();
    })
    .ajaxStop(function() {
        $(this).hide();
    })
;

The ajaxStart/Stop functions will fire whenever you do any Ajax calls.

Update: As of jQuery 1.8, the documentation states that .ajaxStart/Stop should only be attached to document. This would transform the above snippet to:

var $loading = $('#loadingDiv').hide();
$(document)
  .ajaxStart(function () {
    $loading.show();
  })
  .ajaxStop(function () {
    $loading.hide();
  });

Solution 2:

For jQuery I use

jQuery.ajaxSetup({
  beforeSend: function() {
     $('#loader').show();
  },
  complete: function(){
     $('#loader').hide();
  },
  success: function() {}
});

Solution 3:

You can just use the jQuery's .ajax function and use its option beforeSend and define some function in which you can show something like a loader div and on success option you can hide that loader div.

jQuery.ajax({
    type: "POST",
    url: 'YOU_URL_TO_WHICH_DATA_SEND',
    data:'YOUR_DATA_TO_SEND',
    beforeSend: function() {
        $("#loaderDiv").show();
    },
    success: function(data) {
        $("#loaderDiv").hide();
    }
});

You can have any Spinning Gif image. Here is a website that is a great AJAX Loader Generator according to your color scheme: http://ajaxload.info/

Solution 4:

You can insert the animated image into the DOM right before the AJAX call, and do an inline function to remove it...

$("#myDiv").html('<img src="images/spinner.gif" alt="Wait" />');
$('#message').load('index.php?pg=ajaxFlashcard', null, function() {
  $("#myDiv").html('');
});

This will make sure your animation starts at the same frame on subsequent requests (if that matters). Note that old versions of IE might have difficulties with the animation.

Good luck!

Solution 5:

If you are using $.ajax() you can use somthing like this:

$.ajax({
  url: "destination url",
  success: sdialog,
  error: edialog,
  // shows the loader element before sending.
  beforeSend: function() {
    $("#imgSpinner1").show();
  },
  // hides the loader after completion of request, whether successfull or failor.             
  complete: function() {
    $("#imgSpinner1").hide();
  },
  type: 'POST',
  dataType: 'json'
});

Although the setting is named "beforeSend", as of jQuery 1.5 "beforeSend" will be called regardless of the request type. i.e. The .show() function will be called if type: 'GET'.