gistfile1.aw

<?php
/*
Plugin Name: Test
*/
class My_Like_Button {

	function __construct()
	{
		$this->hooks();
	}
	
	function hooks()
	{
		add_action( 'wp_head', array( $this, 'js' ) );
		add_action( 'wp_ajax_register_like', array( $this, 'handle_like' ) );
	}
	
	function js()
	{
		wp_enqueue_script( 'jquery' );
		wp_print_scripts();
		?>
		<script>
		jQuery(document).ready(function(){
			
			jQuery('#like_this_post').click(function(){
				var like_post_id = jQuery('#like_post_id').val();
				var like_user_id = jQuery('#like_user_id').val();
			
				jQuery.post(
					'<?php echo get_option('siteurl') . '/wp-admin/admin-ajax.php' ?>',
					{
						action		: 'register_like',
						user_id		: like_user_id,
						post_id		: like_post_id,
						_wpnonce	: '<?php echo wp_create_nonce('nonce-register_like'); ?>',
					},
					function(response) {	
						alert(response);
					}
				);
				
			});
		});
		</script>
		<?php
	}
	
	function like_button()
	{
		if( !is_user_logged_in() )
			return false;
		
		global $current_user;
		
		$html = '<form action="" method="post">
			<input type="hidden" name="like_post_id" id="like_post_id" value="' . get_the_ID() .'">
			<input type="hidden" name="like_user_id" id="like_user_id" value="' . $current_user->ID . '">
			<input type="button" name="like_this_post" id="like_this_post" value="Like" />
		</form>';
		return $html;
	}
	
	function handle_like()
	{
		global $wpdb;
		$user_id = (int) $_POST['user_id'];
		$post_id = (int) $_POST['post_id'];
		
		if( !is_user_logged_in() )
			return false;
		
		if( !wp_verify_nonce( $_POST['_wpnonce'], 'nonce-register_like' ) )
			die( 'Go away, asshole!' );
		
		/* 
			Here is where we do some sort of database operation to associate
			the Like of the given post with the user who performed the action
		
			Make sure you check for errors. In order to return data, you must
			echo something that the originating page can see. True or false
			only makes sense on this page and not back there.
			
			Typically, you'd output some sort of JSON, XML or plain text.
		*/
		$meta_id = add_post_meta( $post_id, 'user_liked', $user_id );
		if( !$meta_id )
			echo "Like not recorded";
		else
			echo "Like recorded";
		exit;
	}
}

$my_like_button = new My_Like_Button;

Nice article. THx