classes.js

Initializable = function(sender){
  var initialized = false;
  
  sender.isInitialized = function(){
      return initialized;
  };

  sender.setInitialized = function(){
      initialized = true;
  };
  
}

Klass = function(){
  var priv = 1;
  
  // Mixins
  new Initializable(this);
  
  this.getPrivate = function(){
    return priv;
  }
}

k = new Klass;
assert.ok(k);
assert.equal(1, k.getPrivate());
assert.equal(null, k.priv);

assert.ok(!k.isInitialized());
k.setInitialized();
assert.ok(k.isInitialized());