function DemoClasss(){

    var privateVar = "private var";

    this.publicVar = "public var";

    var privateMethod = function(){

        alert( privateVar );

        alert( this.publicVar ); // error, can't access public var, because can't refer correct this var

    }

    this.publicMethod = function() {

        alert( privateVar );

        alert( this.publicVar );      

        privateMethod();

    }

}

var demo = new DemoClasss();

demo.publicMethod();