Wordpress Ajax Setup ( from http://www.bobz.co/ajax-filter-posts-tag/ )

functions.php

function ajax_setup_scripts() {
	// Register and Enqueue Script
  wp_register_script('afp_script', get_template_directory_uri() . '/js/scripts.js', false, null, false);
  wp_enqueue_script('afp_script');
  
  wp_localize_script( 'afp_script', 'afp_vars', array(
		  'afp_nonce' => wp_create_nonce( 'afp_nonce' ), 
			'afp_ajax_url' => admin_url( 'admin-ajax.php' ),
		)
	);
}
add_action('wp_enqueue_scripts', 'ajax_setup_scripts', 100);


function ajax_setup( $vars ) {
	// Verify nonce
  if( !isset( $_POST['afp_nonce'] ) || !wp_verify_nonce( $_POST['afp_nonce'], 'afp_nonce' ) )
  die('Permission denied');

	$vars = $_POST['vars'];
	echo $vars;

  die();
}
add_action('wp_ajax_setup', 'ajax_setup');
add_action('wp_ajax_nopriv_setup', 'ajax_setup');

scripts.js

jQuery(document).ready(function($) {
  // data to pass to function
  data = {
    action: 'setup', // function to execute
    afp_nonce: afp_vars.afp_nonce, // wp_nonce
    vars: 'Data goes here',
  };
  
  // pass data to function and log response
  $.post( afp_vars.afp_ajax_url, data, function(response) {
    if( response ) {
      console.log(response);
    };
  });
});