JavaScript scope - demo showing JS private, privileged, etc. scope

foo.js

var FooWrapper = (function() {

  // private module scope, shared among all Foo instances
  var _private1 = "private1";
  var _private3 = "private3";

  var Foo = function(arg1, arg2, arg3) {

    // private instance var, only visible to privileged methods
    var _private2 = "private2";
    var _private4 = arg2 + " " + arg3;

    // public var; available to anyone anywhere
    this.arg1 = arg1;

    // private module scope + shared among all instances
    // multiple constructor calls will overwrite this
    _private3 = arg1;


    this.getPrivileged1 = function() {
      return _private1 + _private2;
    }

    this.getPrivileged2 = function() {
      return _private4;
    }

    this.getPrivileged3 = function() {
      process.nextTick(function() {
        console.log("in callback => ");
        console.log("\t _private1: ", _private1);
        console.log("\t _private2: ", _private2);
        console.log("\t _private3: ", _private3);
        console.log("\t _private4: ", _private4);
        console.log("\t ");
      })
    }
  }

  Foo.prototype.getPublic1 = function() {
    // _private2, _private4 is undefined
    return _private1;
  }

  Foo.prototype.getPublic2 = function() {
    return _private3;
  }

  // hangs off the class; public
  Foo.classproperty = "zing";

  return Foo;
  
})();

module.exports = FooWrapper;

foo.test.js

// written for mocha

var Foo = require('./foo.js')
  , sinon = require('sinon')
  , should = require('should')
  , util = require('util');

describe("Foo", function() {
  it("should access privileged / public methods", function(done) {
    
    var foo = new Foo();

    foo.getPrivileged1().should.eql('private1private2');

    foo.getPublic1().should.eql('private1');
    
    should.not.exist(foo.getPublic2());
    should.not.exist(foo.arg1);

    var foo2 = new Foo("a", "b", "c");
    foo2.arg1.should.eql("a");

    // this will overwrite the shared variable
    var foo3 = new Foo("1", "2", "3");
    foo3.arg1.should.eql("1");

    // foo3 constructor overwrites foo2's arg "a"
    foo2.getPublic2().should.eql("1");
    foo2.arg1.should.eql("a");

    foo3.getPublic2().should.eql("1");
    foo3.arg1.should.eql("1");

    foo.getPrivileged3();
    foo2.getPrivileged3();
    foo3.getPrivileged3();

    done();
  });
});