Character counter for ACF WYSIWYG Field

acf-field-wysiwyg-character-counter.php

/* For usage with acf_form() */

function my_acf_wysiwyg_character_counter() {
?>
<script type="text/javascript">
acf.add_filter('wysiwyg_tinymce_settings', function(mceInit) {
    mceInit.elementpath = false;
    mceInit.setup = function(ed) {
        var characterLimit = 800,
            edContainer,
            countChar,
            colorOriginal;

        ed.on('init', function(e) {
            edContainer = $(ed.iframeElement).closest('.acf-input');
            countChar = edContainer.find('.mce-statusbar .mce-flow-layout')
                .prepend('<div class="mce-path mce-flow-layout-item mce-first count-char"><span class="count-char-current">0</span><span>/' + characterLimit + '</span></div>')
                .find('.count-char-current');
            colorOriginal = countChar.css('color');
        });

        var limit = function(e) {

            var node = ed.getBody(),
                text = (node.innerText || node.textContent),
                textTrim = text.trim(),
                length = (textTrim.length === 0) ? 0 : text.length;

            if (length > characterLimit) {
                countChar.css('color', 'red');
            } else {
                countChar.css('color', colorOriginal);
            }

            countChar.text(length);
        };

        ed.on('change', limit);
        ed.on('keyup', limit);
    };

    return mceInit;

});
</script>
<?php
}

add_action('acf/input/admin_footer', 'my_acf_wysiwyg_character_counter');

I'd rename this to "Character Counter". Works well then :)