CodeIgniter function that catches if the current request is an Ajax one.

is_ajax.php

<?php
/**
 * Is Ajax
 * 
 * Returns true or false depending on if the http request was an ajax one or not.
 * 
 * @return boolean
 */
if(!function_exists('is_ajax')){

  function is_ajax(){

		$ci =& get_instance();

		return $ci->input->is_ajax_request();

	}

}