One of the best tutorials on private and protected access in javascript is here: http://javascript.crockford.com/private.html.
function Foo(a) {
var bar = a; // private instance data
this.getBar = function() {return(bar);} // methods with access to private variable
this.setBar = function(a) {bar = a;}
}
var x = new Foo(3);
var y = x.getBar(); // 3
x.setBar(12);
var z = x.bar; // not allowed (x has no public property named "bar")