PHP: WP excerpt character counter

excerpt_count.php

<?php
// Excerpt character count
function excerpt_count_js() { ?>
    <script>
    jQuery(document).ready(function ($) {
        var counterVal = $('#excerpt-counter input').val($('#excerpt').val().length);

        $('#postexcerpt .handlediv').after('<div id="excerpt-counter"><small>Excerpt length: </small> <input type="text" value="0" maxlength="3" size="1" readonly> <small>character(s)</small></div>');
        counterVal
        
        $('#excerpt').on('keyup', function () {
            counterVal
        });
    });
    </script>
    
    <style>
    #excerpt-counter {
        position: absolute;
        top: 2px;
        right: 30px;
        color: #666;
    }
    #excerpt-counter input {
        background: #f2f2f2;
    }
    </style>
    <?php
}

add_action( 'admin_head-post.php', 'excerpt_count_js' );
add_action( 'admin_head-post-new.php', 'excerpt_count_js' );