Need help using prototypeJS

I have some issue with prototypeJS today which I am using for a new project so here's my code :

var div = $('addcontact');
Event.observe(div, 'click', respondToClick);
function respondToClick(event) {    
    var form = $('contactForm');
    form.setStyle(
          {display : initial}
    );
}

I don't understand why it is not working, $('contactForm') has a display : none as a css property, so what I want to do is display it when clicking on $('addcontact').