Character count for WordPress content and excerpt fields

UPDATE (2014-04-24 09:36): I've corrected the JS code by adding a check for the existence of the excerpt and the word counter entries; without this, JS would fail to load on pages and custom posts.

I've been looking for a simple letter counter for the WordPress content & excerpt fields, but the only plugin I've found is not working as of WordPress 3.8¹. I've also come across with a blog post how to do this for the exceprt², but that was throwing errors, so I corrected it and added the content counter.

Add this to your theme's functions.php:

/* letter counter */
add_action( 'admin_head-post.php',  'letter_count_js'));
add_action( 'admin_head-post-new.php',  'letter_count_js' ));

public function letter_count_js(){
    echo '<script>jQuery(document).ready(function(){

        if( jQuery("#excerpt").length ) {
            jQuery("#postexcerpt .handlediv").after("<input type='text' value='0' maxlength='3' size='3' id='excerpt_counter' readonly='' style='background:#fff; position:absolute;top:0.2em;right:2em; color:#666;'/>");
            jQuery("#excerpt_counter").val(jQuery("#excerpt").val().length);
            jQuery("#excerpt").keyup( function() {
                jQuery("#excerpt_counter").val(jQuery("#excerpt").val().length);
            });
        }

        if( jQuery("#wp-character-count").length ) {
            jQuery("#wp-word-count").after("<td id='wp-character-count'>Character count: <span class='character-count'>0</span></td>");
            jQuery("#wp-character-count .character-count").html(jQuery("#wp-content-wrap .wp-editor-area").val().length);
            jQuery("#wp-content-wrap .wp-editor-area").keyup( function() {
                jQuery("#wp-character-count .character-count").html(jQuery("#wp-content-wrap .wp-editor-area").val().length);
            });
        }

    });</script>';
}

(Oh, by the way: this entry was written by Peter Molnar, and originally posted on petermolnar dot net.)