It will be nice if cursor.each() will check for return code of callback. Based on this it should escape from iteration. See http://api.jquery.com/each for example of such API.

Usa case: get only 20 documents, for example

items = []
cursor.each(function(err, item) {
   if (err != null)
      return false;
   items.push(item);
   if (items.length >= 20) {
     return false;
   }
   return true;
});