how to have Javascript Object creation pattern with Reusable methods and private properties?

Considering object creation patterns with private properties, one way to do is :

function MyStack (){
    var list = [],
        index = 0;

    this.push =  function(val){ 
        return list[index++] = val;
    };
    this.pop = function(){// ...}
}

var stack1 = new MyStack();       stack1.push(5);
var stack2 = new MyStack();       stack2.push(11);

Problem with this: Every instance of Stack has it's own copy of methods 'push' and 'pop'.

Another way for implementing constructor method is:

function MyStack(){ 
    this.list = []; 
    this.index = 0;
}
MyStack.prototype = {
    insert: function(val){
            return this.list[this.index++] = val;
        },
    pop:function(){//...}
}

Problem here: We lose the privacy of list and index.

Is there a way, such that we can have both methods reuse among instances and privacy of properties ?

I understand that we can have this for methods that don't operate on any state of the object, but I am talking more about those methods that do operate on the state.