Simple jQuery character countdown in textarea

Looking to build a Twitter-like textarea character countdown to show your users how much space they have remaining? Good. See the below implementation using jQuery:

$(document).ready(function() {
  var maxCharacters = 255;
  document.getElementById('description').onkeyup = function() {
    document.getElementById('characters-counter').innerHTML = (maxCharacters - this.value.length);
  };
});

Easy, right? You can view the full demo of this implementation working on: http://codepen.io/jonathanbrizio/pen/pbYZZy/