Drupal 7 has introduced several new techniques that allow you far greater flexibility and control in the scripts you can have on your Drupal
Ajax is a type of functionality that enables your pages to retrieve information from a resource on the server without the need to reload.
Adding a different version of jQuery for your codebase with its own identifier.
Creating custom Drupal.ajax object 'on the fly' and attach it to any DOM element on the page (div, td, span etc.)
Add AJAX capability to a new DOM element
Example Code snippet to create ADD MORE BUTTON with drupal 7 form API
Simple Drupal AJAX load with jQuery and delivery callback