this.find({},{
    "updated_at":1,
    "created_at":1,
},callback);

this.aggregate([{
    $project:{
        "updated_at" :1,
        "created_at" :1,
    }
}],callback);

// lets say query result is in dataArray

var created_at = moment(dataArray[0].created_at);
var created_at_est = created_at.clone().tz("America/New_York");
dataArray[0].created_at = created_at_est.format('ddd MMM DD YYYY HH:mm:ss');
console.log(dataArray[0].created_at);
// result is string in aggregate query and object in find query