Library threads-ajax-pagination.js contains a simple way of implementing ajax navigation and body class management on WordPress websites. Just make sure to set the right classes within the script to select the appropriate div to change on click and add the .ajaxlink class to any INTERNAL link within the website that you want to ajaxify.
Link title must contain the page web name, as titles can be dinamically passed through the #js-pageTitle ID.
Loader and loader icon can be customized through css.
Links outside the main div will retain the current class and can be styled accordingly.