function onoff(menu){

  var link    = document.getElementById(menu);
  var element = document.getElementById(menu + "_div");

  if(element && (element.style.display == 'none' || element.style.display == '')){
    menuOpen(element,link);
    closeOthers(menu);
  } else if(element) {
    menuClose(element,link);
  }
  return false;
}

function menuOpen(element,link){
  if(element) element.style.display = 'block';
  if(link) link.className = 'open';
}

function menuClose(element,link){
  if(element) element.style.display = 'none';
  if(link) link.className = '';
}

function closeOthers(menu){
  for(var i in menus){
    var j = menus[i];
    var link    = document.getElementById(j);
    var element = document.getElementById(j + "_div");
    if(menu != j){
      menuClose(element,link);
    }
  }
}

var menus = ['menu1', 'menu2','menu3', 'menu4','menu5', 'menu6'];