a.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var schema = Schema({ name: String });
module.exports = mongoose.model('User', schema);

b.js

var mongoose = require('mongoose')
var User = require('./a');

User.find(function (err, docs) {
  console.log('found', arguments);
  mongoose.disconnect();
});

init.js

//
// run `node init.js`
//

var mongoose = require('mongoose');

// create "global" connection
mongoose.connect('localhost', 'test-1249');

mongoose.connection.on('open', function () {
  // after opening, create a document
  var A = require('./a');
  A.create({ name: 'woot' }, function (err) {
    if (err) {
      console.error('creation error', err);
      return mongoose.disconnect();
    }
    require('./b')
  });
});