title: jQuery / JS get the scrollbar height of an textarea
body: <p>I've got a textarea with a fixed height. When the user types text into the textarea a scrollbar will show up after the user typed some text in it.</p>
  
  <p>How can I get the scrollbar height using jQuery or plain JavaScript? I've been searching for this for hours, but couldn't find anything. I can't just insert a div and get the scrollbar height via the div offset because a textarea is not allowed to have child elements.</p>
  
  <p>Please don't give me a link to a jQuery Plug-In that does the job. I want to learn something. </p>