passando mangusta come argomento a una funzione

Osservando la documentazione di mongoose connect

Puoi usare Promises.

    var mongoose = require('mongoose');
    var myModule = require('myModule');

    var dbUrl = 'mongodb://localhost:27017/gfsTestDB';

    mongoose.connect(dbUrl)
      .then(
        // The connection is ready to use!
        () => {
          var readyObj = new myModule(mongoose);

          // ...
        },

        // Handle the connection error
        (err) => {
          // ...
        },
      );

Puoi utilizzare le richiamate

    var mongoose = require('mongoose');
    var myModule = require('myModule');

    var dbUrl = 'mongodb://localhost:27017/gfsTestDB';

    mongoose.connect(dbUrl, (err) => {
      if (err) {
        // Handle the error

        // ...

        return;
      }

      // We get successfully connected to the database

      var readyObj = new myModule(mongoose);

      // ...
    });