Lag measure

gistfile1.js

(function() {
  var lastTime = +new Date();
  var avgArr = [];
  var avg;
  setInterval(function() {
    var time = +new Date();
    var diff = time - lastTime;
    lastTime = time;
    if (avg) {
      if (diff > avg * 2) {
        console.log('lag: ', diff + ' ms');
      }
    } else {
      avgArr.push(diff);
      if (avgArr.length >= 100) {
        avg = avgArr.reduce(function(acc, b) {
          return acc + b;
        }, 0) / avgArr.length;
        console.log('avg: ', avg);
      }
    }
  }, 0);
}());