// Closures
var counter = (function(){
  var privateCounter = 0;
  function changeBy(val){
    privateCounter += val;
  }
  return{
    increment: function(){
      changeBy(1);
    },
    decrement: function(){
      changeBy(-1);
    },
    value: function(){
      return privateCounter;
    }
  };
})();

console.log(counter.value());
counter.increment();
counter.increment();
counter.increment();
console.log(counter.value());
counter.decrement();
console.log(counter.value());