function sequence(startCount, newCount) {

  var currentCount = startCount;

  return function counter(startCount, newCount) {

    if (newCount !== undefined) {

      console.log(currentCount);

      currentCount = +newCount;

      return currentCount;

    } else {

      return currentCount++;

    }

  };

}

​

var counter = sequence(1, 3);

​

console.log(counter());

console.log(counter());

​

​