Encapsulation in javascript

SomeClass = function(id) {
    this._id = id;
}
(function() {
    function intFun() {
        return this._id;
    }
    SomeClass.prototype.extFun = function() {
        return incFun();
    }
})();

SomeClass = function (id) {
    var THIS = this; // unambiguous reference
    THIS._id = id;

    var intFun = function () { // private
        return THIS._id;
    }

    this.extFun = function () { // public
        return intFun();
    }
}

MyClass = function(x, y, z) {
   // This is the constructor. When you use it with "new MyClass(),"
   // then "this" refers to the new object being constructed. So you can
   // assign member variables to it.
   this.x = x;
   ...
};
MyClass.prototype = {
    doSomething: function() {
        // Here we can use the member variable that
        // we created in the constructor.
        return this.x;
    },
    somethingElse: function(a) {
    }
};

var myObj = new MyClass(1,2,3);
alert(myObj.doSomething()); // this will return the object's "x" member
alert(myObj.x); // this will do the same, by accessing the member directly

myDiv.onclick = myObj.doSomething;

myDiv.onclick = function() {
    myObj.doSomething.call(myObj);
}

var MyClass = function() {};

MyClass.prototype = {
   _someVar : null,
   _otherVar : null,

   initialize: function( optionHash ) {
                _someVar = optionsHash["varValue"];
                _otherVar = optionsHash["otherValue"];
           },

   method: function( arg ) {
               return _someVar  + arg;
           },
};

var myClass = new MyClass( { varValue: -1, otherValue: 10 } );
var foo = myClass.method(6);