[javascript] Share variables between files in Node.js?

I'm unable to find an scenario where a global var is the best option, of course you can have one, but take a look at these examples and you may find a better way to accomplish the same:

Scenario 1: Put the stuff in config files

You need some value that it's the same across the application, but it changes depending on the environment (production, dev or test), the mailer type as example, you'd need:

// File: config/environments/production.json
{
    "mailerType": "SMTP",
    "mailerConfig": {
      "service": "Gmail",
      ....
}

and

// File: config/environments/test.json
{
    "mailerType": "Stub",
    "mailerConfig": {
      "error": false
    }
}

(make a similar config for dev too)

To decide which config will be loaded make a main config file (this will be used all over the application)

// File: config/config.js
var _ = require('underscore');

module.exports = _.extend(
    require(__dirname + '/../config/environments/' + process.env.NODE_ENV + '.json') || {});

And now you can get the data like this:

// File: server.js
...
var config = require('./config/config');
...
mailer.setTransport(nodemailer.createTransport(config.mailerType, config.mailerConfig));

Scenario 2: Use a constants file

// File: constants.js
module.exports = {
  appName: 'My neat app',
  currentAPIVersion: 3
};

And use it this way

// File: config/routes.js

var constants = require('../constants');

module.exports = function(app, passport, auth) {
  var apiroot = '/api/v' + constants.currentAPIVersion;
...
  app.post(apiroot + '/users', users.create);
...

Scenario 3: Use a helper function to get/set the data

Not a big fan of this one, but at least you can track the use of the 'name' (citing the OP's example) and put validations in place.

// File: helpers/nameHelper.js

var _name = 'I shall not be null'

exports.getName = function() {
  return _name;
};

exports.setName = function(name) {
  //validate the name...
  _name = name;
};

And use it

// File: controllers/users.js

var nameHelper = require('../helpers/nameHelper.js');

exports.create = function(req, res, next) {
  var user = new User();
  user.name = req.body.name || nameHelper.getName();
  ...

There could be a use case when there is no other solution than having a global var, but usually you can share the data in your app using one of these scenarios, if you are starting to use node.js (as I was sometime ago) try to organize the way you handle the data over there because it can get messy really quick.