closure

# closure - private

var counter = function() {
  var privateCounter = 0;
  function changeBy(val) {
    privateCounter += val;
  }
  return {
    increment: function() {
      changeBy(1);
    },
    decrement: function() {
      changeBy(-1);
    },
    value: function() {
      return privateCounter;
    }
  }
};
var counter1 = counter();
counter1.increment();
console.log("counter1:", counter1.value());
var counter2 = counter();
console.log("counter2:", counter2.value());