Visual character limit for textareas

charlimit.js

(function($){
    function addCharLimit(){
         $('textarea').each(function(){
            maxlength = $(this).attr("maxlength");
            if ( maxlength !== undefined ) {
                charContainer = $(this).parent().find('p.charleft').val();
                if ( charContainer === undefined ) {
                    $(this).parent().append("<p class='charleft description'>");
                }
                charleft = maxlength - $(this).val().length;
                $(this).parent().find('.charleft').html(charleft+" characters left.");
            }

            $(this).keyup(function() {
                maxlength = $(this).attr("maxlength");
                if ( maxlength !== undefined ) {
                    charleft = maxlength - $(this).val().length;
                    $(this).parent().find('.charleft').html(charleft+" characters left.");
                }
            })
        });
    }

    acf.add_action('ready append', function( $el ){
        addCharLimit();
    });
})(this.jQuery);

We use this for Advanced Custom Fields, you may need to adjust depending on your markup.

Updated to support dynamically loaded ACF textareas.