Async with For Loop

node_mongo_groups.js

var login_counts = [],
    j = 30,
    // functions scope
    add_count = function (index, query) {
      collection.find({date: query},function (err, cursor) { 
        cursor.count(function (err, count) { 
          login_counts[index] = count; 
        }); 
      });
    };

for (;j>0;j--) { 
  tday.setDate(tday.getDate()+1); 
  yday.setDate(tday.getDate()+1);
  add_count(j, {'$gt':tday, '$lt':yday});
}