Edit in JSFiddle

var simpleCalc = (function () {
    var privateCounter = 1;
    var privateShowCounter = function () {
        console.log('Value of privateCounter: ' + privateCounter);
    };
    var setPrivateCounter = function (a) {
        privateCounter = a;
        privateShowCounter();
    };
    var getPrivateCounter = function (a) {
        return privateCounter;
    };
    var addition = function (a) {
        privateShowCounter();
        console.log('Addition results in: ' + (a + privateCounter));
    };
    var subtraction = function (a) {
        privateShowCounter();
        console.log('Subtraction results in: ' + (a - privateCounter));
    };

    return {
        add: addition,
        sub: subtraction,
        set: setPrivateCounter,
        get: getPrivateCounter
    };
})();
simpleCalc.add(3); // Addition results in: 4
simpleCalc.sub(8); // Subtraction results in: 7
simpleCalc.set(5); // Value of privateCounter: 5
simpleCalc.add(3); // Addition results in: 8
simpleCalc.sub(8); // Subtraction results in: 3
var a = simpleCalc.get();
console.log('Variable to work with: ' + a);
<p>Just open the console to see the output...</p>