Can someone say to me if it's possible to block a textarea.

I explain :
I want to enter only 235 characters in my textarea,for the moment I use a javascript but if you are too fast you can enter more than 235.
So for the moment I resize my textbox to 5*47 charaters but the user can continue If he want,I want to eject the toolbar and stop the user from encoding after 5 lines.