Use the Rewrite API to interpret AJAX requests

gistfile1.aw

<?php

add_action( 'init', function(){

	add_rewrite_rule( '^ajax/([^/]*)/([^/]*)/([^/]*)/([^/]*)/?','index.php?ajax=true&action=$matches[1]&type=$matches[2]&offset=$matches[3]&meta=$matches[4]','top' );
});

add_filter( 'query_vars', function( $query_vars ){

	$query_vars[] = 'ajax';
	$query_vars[] = 'action';
	$query_vars[] = 'cat';
	$query_vars[] = 'offset';
	$query_vars[] = 'meta';
	return $query_vars;
});

add_action( 'template_redirect', function() {

	// Don't do anything unless this is an AJAX request
	if ( !get_query_var( 'ajax' ) )
		return;

	$my_data = array(
			'action' => sanitize_key( get_query_var( 'action' ) ),
			'type' => sanitize_key( get_query_var( 'cat' ) ),
			'offset' => intval( get_query_var( 'offset' ) ),
			'meta' => sanitize_key( get_query_var( 'meta' ) ),
		);
	echo json_encode( $my_data );
	die();

});