Two Factor Timer

2f-two-factor-timer.js

var updateTimer = function(period, updateTokenCallback) {
  // Get current time seconds
  var epocSecs = Math.floor((+new Date()) / 1000);
  var sec = epocSecs % period;

  var secsToNext = 0;

  // Fire if clock has struck 0 or 'period'
  if (sec == 0 || sec == period) {
    updateTokenCallback();
  } else {
    // If less than 'period', next update is at 'period'
    if (sec < period) {
      secsToNext = period - sec;
    } else if (sec > period) {
      secsToNext = period - sec;
    }
  }
  
  return secsToNext;
};

var myTimer = function() {
  var secsToNext = updateTimer(30, function() { console.log("Updating token...") });
  console.log("Your token expires in: " + secsToNext);
};

setInterval(myTimer, 500);