Node.Js - letting users know someone is typing something

Question

i'm having this chat app where i would like to add iMessage/Facebook feature where people know when each others are typing something, by changing their name's color e.g.

I have tried this :

$messageBox.keydown(function(){
        if($(this).val().length!=0){ socket.emit('writing_message')};
            });

        socket.on('showing_writers',function(){
        $users.html('');  // that was just to test if the event was well received, which is not the case...
        });

I was hoping that this way, everytime a user presses a letters, it would trigger a very basic event on the server, which would respond to everyone like that :

socket.on('writing_message',function(){
    io.sockets.emit('showing_writers', socket.nickname);
    }

socket.nickname contains the user's nickname which I will use to find him back on all client's files, in order to change his name's color.

Does anyone know how to do it in a better way, and why what i'm doing is not working ?