Change submit button to a loading image with jquery

Go the simplest way. Say your button is btnSubmit.

<asp:Button ID="btnSubmit" runat="server" OnClick="btnSubmit_Click" Text="Submit" />
<div id="divMsg" style="display:none;">
    <img src="../images/loading.gif" alt="Please wait.." />
</div>

Now using jquery, on click of the button:

<script type="text/javascript">
     $('#btnSubmit').click(function(){
         $(this).attr('disabled','disabled');
         $('#divMsg').show();
         //your client side validation here
         if(valid)
            return true;
         else
            {
              $(this).removeAttr('disabled');
              $('#divMsg').hide();     
              return false;
            }
     });
</script>

The submit button will be disabled, the animating image loading.gif will show up. And the page will postback. The benefit is that if validation fails you can again enable the submit button and hide the loading image. In such case, obviously you will show the error message.

Although simply replacing the submit with an image might work, removing the button might prevent the submit input's value from being sent (like when it's disabled). This can cause problems for some applications that rely on the submit's value being sent to the server - for example testing which submit button the user has pressed or using the same controller for many actions.

For those cases, you can use another method that works just as good - hiding the submit and adding an image:

$(document).ready(function() {
    $('input[type="submit"]').click(function() {
        $(this).css('display', 'none');
        $('<img>').attr('src', 'http://www.mayla.ro/App_Themes/Glass/Editors/Loading.gif').insertAfter($(this));
    });
});

My way of doing this:

$(document).ready(function () {
    $('.class_name').click(function () {
        $(this).parent().append('<img src="data:image/gif;base64,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" />');
        $(this).hide();
    });
});