namespacingPrivateFunctions.js

var dwightSalary = (function() {
    var salary = 60000;
    function changeBy(amount) {
        salary += amount;
    }
    return {
        raise: function() {
            changeBy(5000);
        },
        lower: function() {
            changeBy(-5000);
        },
        currentAmount: function() {
            return salary;
        }
    }; 
})();

alert(dwightSalary.currentAmount()); // $60,000
dwightSalary.raise();
alert(dwightSalary.currentAmount()); // $65,000
dwightSalary.lower();
dwightSalary.lower();
alert(dwightSalary.currentAmount()); // $55,000

dwightSalary.changeBy(10000) // TypeError: undefined is not a function