[jQuery] textarea with line number

[furionn]

Hi all. I am noob in Jquery. Help pls.
How to make textarea with line number ?

Here is my code:

<script type="text/javascript">
function f1()
 {
                var lines = $('#txt').val().split('\n');
                var line_number_size = $('#line_number li').size()+1;
                var max = lines.length;

                if(max >= line_number_size)
                {
                    $('<li>' + line_number_size + '</li>').appendTo
('ul#line_number');
                    line_number_size++;
                }
                else
                {
                  $('li:last').remove();
                  line_number_size--;
                }
}
</script>
<ul id="line_number">
            <li>1</li>
            <li>2</li>
            <li>3</li>
        </ul>
<textarea id="txt" class="txt" rows="20" cols="50" onkeydown="f1();"></
textarea>