Countdown

gistfile1.txt

function countdown(seconds, callback){
  var i = setInterval(function() {
    if (typeof callback === 'function') {
      callback(seconds--);
    } else {
      console.log(seconds--);
    }

    if (seconds === -1) {
      clearInterval(i);
    }
  }, 1000);
}

countdown(5);
countdown(10, function (i) {
  console.log('THIS IS MY CUSTOM CALLBACK!!!', i);
});