promise vs seq

gistfile1.txt

RealtimeSync.prototype._storeDirectMessage = function(message, user, callback) {
  var messageDate = new Date(Date.parse(message.created_at)),
      b = user.user_id, privateMsg;
  
  if(!user.dm_latest_d) {
    user.dm_latest_d = new Date(0);
  }
  
  if(messageDate < user.dm_latest_d) {
    return;
  }
  
  var promises = [],
      msgSavedDef = new promise.Def();
  
  promises.push(msgSavedDef);

  db.PrivateMessage.findOne({ b: b, i: message.id_str }, function(err, t){
    if(!t) {
      t = new db.PrivateMessage();
      t.b = b;
      t.createFromJSON(message);

      t.save(function () {    
        msgSavedDef.resolve(t.toPublicObject())
      });
    }
  });
  
  if(messageDate > user.dm_latest_d) {    
    var userSavedDef = new promise.Def();
    
    promises.push(userSavedDef);

    user.dm_latest_d = messageDate;
    user.dm_latest_id = message.id_str;
    user.save(function() {
      userSavedDef = new promise.Def();
    })
  }

  promise.all(promises).then(function(d) {
    if(d[0]) {
      callback(d[0])
    }
  })
}