Singleton pattern implemented in NodeJS. Example: Shared database like neDB or MongoDB, Application configuration, Filter...

Singleton.js

/***
 * NodeJS module that implements the single pattern.
 * http://en.wikipedia.org/wiki/Singleton_pattern
 * 
 * The goals is to create the object: instance only one time
 *  thus the instance is shared in the source code. 
 * 
 * You must be aware that there is a risk to break
 *  the isolation principles.
 */
if(!global.instance)
{
 var instance = {};
 instance.state = false;
 instance.func1 = function(state){
   instance.state = state;
 };
 global.instance = instance;
}
 
exports.instance = global.instance;

SingletonTest.js

/***
 * Test singleton instance.
 * 
 * - File must be created under directory: test/
 * - Depedencies
 * $npm install mocha expect
 * - Run tests.
 * $mocha
 */
var expect = require('expect');
 
describe("Singleton", function()
{
  it("Implementation", function()
  {
    // Check default state 
    expect(require('../Singleton').instance.state).toBe(false);
 
    // Change the state of the instance (shared everywhere)
    require('../Singleton').instance.func1(true);
 
    // Check if the new state has been propagated to the instance itself
    expect(require('../Singleton').instance.state).toBe(true);
  });
});