Followwing setup will use Spin.js instead of loading animation gif.
Make sure that you loaded Spin.js before setup.
$(function(){
$.ui.domwindowdialog.setup({
width: 600, // dialog width
height: 300, // dialog height
spinjs: true // make this true to use spin.js
});
});
<a
class="apply-domwindow-open"
href="dialog1.html"
data-domwindow-ajaxdialog="true"
>open</a>