Example of private data in a closure in javascript

closures.js

var lib = (function (win) {
    var sum = 0;

    return {
        makeSum: function (arr) {
            win.document.body;

            JSoop.each(arr, function (value, index) {
                sum = sum + value;
            });

            return sum;
        }
    };
}(window));

lib.makeSum([1, 2, 3]); //6

lib.makeSum([1, 2, 3]); //12