No-Spam-Registration-with-JavaScript.php

<?php
/**
  * Plugin Name: No Spam Registration with JavaScript
  * Plugin URI:  http://blog.samelh.com
  * Description: Prevents spam registration on your WordPress blog/website by adding a necessary form field with JavaScript on document load
  * Author:      Samuel Elh
  * Author URI:  http://samelh.com
  * Version:     0.1
  */

add_action('register_form', 'se_nospam_register_append_input');
add_action('register_post', 'se_nospam_register_validate', 10, 3);

if ( !function_exists('se_nospam_register_append_input') ) :;
function se_nospam_register_append_input()
{
?>
	<script type="text/javascript" id="se_nospam_inline_js">
		window.onload = function() { // it's all about this JS, once JS is loaded, the spamcheck field will be available..
			var e = document.getElementById('se_nospam_inline_js');
			if ( null !== e ) {
				e.outerHTML = '<input id="process-register" type="hidden" name="process-register" value="<?php echo wp_create_nonce( 'se-nospam-register' ); ?>" />';
			} return;
		}

	</script>
<?php
}
endif;

if ( !function_exists('se_nospam_register_validate') ) :;
function se_nospam_register_validate( $login, $email, $errors )
{

	$die_message = apply_filters( "se_nospam_register_error", "Are you spamming?<br/><br/> <a href=\"javascript: window.history.go(-1);\">&laquo; Go back</a>" );

    if( !isset($_POST['process-register']) ) {
    	wp_die( $die_message );
        // or just: $errors->add( 'empty_realname', "<strong>ERROR</strong>: Are you spamming?" );
    }

    else if( empty($_POST['process-register']) )
    {
    	wp_die( $die_message );
        // or just: $errors->add( 'empty_realname', "<strong>ERROR</strong>: Are you spamming?" );
    }

    else if(!wp_verify_nonce($_POST['process-register'], 'se-nospam-register'))
    {
    	wp_die( $die_message );
        // or just: $errors->add( 'empty_realname', "<strong>ERROR</strong>: Are you spamming?" );
    }

    return $errors;
}
endif;