Hide a message for an entire session

friendly_hider.js

var message_box = 'item42';
var jar = new CookieJar({expires: ''});
//you can also set expires to any number of seconds
if(!!jar.get('hide_message')){
  $(message_box).hide();
}else{
  jar.put('hide_message',true);
  $(message_box).observe(
    'click',
    function(evt){
      this.hide();
    }
  ).setStyle('cursor:pointer');
};