var NEWMARK = '<span class="New">←New!</span>';

function addNewMarkToMenu(dates){
  for (var category in dates) {
    if(diff(dates[category]) <= 3){
      document.getElementById('menu_' + category).innerHTML += NEWMARK;
    }
  }
}

function addNewMarkToBookshelf(dates){
  var list = document.getElementById('CategoryList');
  for (var category in dates) {
    if(diff(dates[category]) <= 3){
      document.getElementById('Submenu_' + category).firstChild.innerHTML += NEWMARK;
      if(list){
        document.getElementById('CategoryList_Title_' + category).className += ' new';
      }
    }
  }
}

function diff(ymd){
  y = ymd/10000;
  m = ymd/100 % 100;
  d = ymd % 100;
  return Math.floor((new Date() - new Date(y,m-1,d)) / (60*60*24*1000));
}