toJSON_Plugin.js

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

console.log('\n===========');
console.log('    mongoose version: %s', mongoose.version);
console.log('========\n\n');

var dbname = 'testing_tojson';
console.log('dbname: %s', dbname);
mongoose.connect('localhost', dbname);
mongoose.connection.on('error', function () {
  console.error('connection error', arguments);
});




var schema = new Schema({
    name: String
});
//schema.set('toJSON', { hide: '_id' })

// overriding toJSON
var toJSON = mongoose.Document.prototype.toJSON;
schema.methods.toJSON = function (opts) {
  var ret = toJSON.apply(this, arguments);
  var hide = opts && opts.hide
          || this.schema.options.toJSON && this.schema.options.toJSON.hide;

  if (hide) {
    hide.split(' ').forEach(function (prop) {
      delete ret[prop];
    });
  }

  return ret;
}


var A = mongoose.model('A', schema);

mongoose.connection.on('open', function () {
  var a = new A({ name: 'tojson' });

  /**
   * Test our plugin
   */

  //console.log('hidden', a.toJSON())
  console.log('hidden', a.toJSON({ hide: '_id' }))


  a.save(function (err, a) {
    if (err) return done(err);

    A.findById(a, function (err, doc) {
      console.error('found', doc);
      done(err);
    });
  })
});

function done (err) {
  if (err) console.error(err.stack);
  mongoose.connection.db.dropDatabase(function () {
    mongoose.connection.close();
  });
}