Query with variables not working using nodejs ,express, mongojs and mongodb

My application needs to get the result of this query (this is already giving the correct result in mongoDb):

  var denominator = db.getCollection('Transactions').aggregate({
     $group: { 
        "_id": null, 
        "Alltotal": {$sum:"$transAmount"}
     }
   };
  db.getCollection('Transactions').aggregate([{
  $group: { 
    _id: '$merchantCode', 
    total: {
        $sum: { $multiply: ['$transAmount', 100 ]}

 }}},
   { $project: { 

       percentage: { 
         $divide: [ 
           "$total", 
          denominator.toArray()[0].Alltotal
          ] 
      } 
   }
 }
])

Now here is how I am trying to execute it:

  var express = require('express');
  var app = express();
  var mongojs = require('mongojs');
  var dbTransaction = mongojs('dataAnalysisDb',['Transactions']);

  app.get('/Transactions',function(req,res){

  var denominator = dbTransaction.Transactions.aggregate([{
                    $group: {
                           _id: 'null',
                           total: { $sum: '$transAmount' }
                         }
                      }]);
   dbTransaction.Transactions.aggregate([{
    $group: {
        _id: '$mtype',
        total: {
            $sum: { $multiply: ['$transAmount', 100 ]}

     }}},
       { $project: {
           percentage: {
             $divide: [
               "$total",
               denominator.toArray()[0].total
              ]
          }
       }
    },
     { $sort : { _id : 1, posts: 1 } }
   ], function(err,docs){
    console.log(docs); //this is for testing
    res.json(docs);
   });
 });

I think this is not working because I am not sending the variable in the correct way to the server and when I use it on the operation it is not defined. I will appreciate any suggestion on how to fix it. Thank you

via R.martin