django admin textarea widget char counter

admin.py

# admin
from django import admin
from django.db import models
from widget import TextareaWithCounter

class MyModelAdmin(admin.ModelAdmin):
    formfield_overrides = {
        models.TextField: {'widget': TextareaWithCounter},
    }
    class Media:
        css = {
            "all": ("textareacounter/textareacounter.css", )
        }
        js = ("textareacounter/textareacounter.js", )

textareacounter.css

.counter {
    display: inline-block;
    vertical-align: bottom;
    margin-left: 10px;
}

.counter .input-counter {
    font-weight: bold;
}

textareacounter.js

(function($) {
    $(function() {
        $('textarea.textareacounter').change(function(e) {
            e.preventDefault();
            $(this).siblings('.counter').find('.input-counter').html(
                $(this).val().length
            );
        });
        $('textarea.textareacounter').keyup(function(e) {
            $(this).change();
        })
    })
})(django.jQuery);

widget.py

# wiget 

from django.forms.widgets import Textarea


class TextareaWithCounter(Textarea):

    def render(self, name, value, attrs=None):
        attrs.update({'class': 'textareacounter'})
        ret_html = super(TextareaWithCounter, self).render(name, value, attrs)
        return ('{}<div class="counter"><span class="input-counter">'
                '{}</span> chars</div>').format(ret_html, len(value))