I want to make a textbook where it starts out as a given width/height. Then if users type more then the given amount of space, the textbox expands downward. How do I go about doing this? Do I use css? The basic textbox just displays a scroll bar when users pass the number of rows allow. How do I make it so the textbox expands the rows by say 5 more?

<form method="post" action="">
<textarea name="comments" cols="50" rows="5"></textarea><br>
<input type="submit" value="Submit" />
</form>

How do i use the example that Robert Harvey mentioned? I never used javascript before..