jQuery / JS get the scrollbar height of an textarea

Question

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.

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.

Please don't give me a link to a jQuery Plug-In that does the job. I want to learn something.

Answer 1

textarea.scrollHeight

returns an integer (pixels)

Answer 2

$.each($("textarea"), function () {
    var scrollHeight = parseInt(this.scrollHeight);
    if ($("this").val() != "" && isNaN(scrollHeight) == false && scrollHeight > 0 && scrollHeight > $(this).height()) {
        console.log($(this).attr("id"));
        $(this).height(scrollHeight);
    }
});