module.js

var app = (function(w, d){
  var myPrivateVariable = "My private content";
  
  var __private = {
    cache : function(){ 
      this.link = d.querySelector('.link-item');
    }
    bind  : function(){ 
      this.link.addEventListener('click', this.handleClick, false);
    },
    
    handleClick: function(){
      console.log(myPrivateVariable);
    }
  };
  
  var app = {
    init: function(){
      console.log(myPrivateVariable);
      
      __private.cache();
      __private.bind();
    }
  };
  
  return app;
})(window, document);

app.init(); //init the app
console.log(myPrivateVariable); // undefined