var Product = (function () {
    var cost = 1000
    ,tax = 0.05
    ,price = function () {
        return cost * (tax + 1);
    }
    ,main = function () {
    };
    main.prototype = {
        tax: function (n) {
            tax = n;
        }
        ,price : function () {
            var p = price();
            var t = cost * tax;
            return [p,t,p-t];
        }
    };
    return main;
})();
 
var product = new Product();
console.log(product.price());//[1050,50,1000]
product.tax(0.08)
console.log(product.price());//[1080,80,1000]