Javascript timer progress bar

Question

I have timer function, with progress bar. It works well, but I want make a smooth progress bar animation, with 60 FPS

function started(duration) {
    var TotalSeconds = 40;
    var documentWidth = $(document).width();
    var start = Date.now();
    var intervalSetted = null;

    function timer() {
        var diff = duration - (((Date.now() - start) / 1000) | 0);
        var seconds = (diff % 60) | 0;
        seconds = seconds < 10 ? "0" + seconds : seconds;
        $('#timer').html("00:" + seconds);
        var progresBarWidth = (seconds * documentWidth / TotalSeconds);

        $('#progress').css({
            width: progresBarWidth + 'px'
        });

        if (diff <= 0) {
            clearInterval(intervalSetted);
        }
    }

    timer();
    intervalSetted = setInterval(timer, 1000);
}

started(40);

How can I achieve 60FPS animation?

Here is demo of my code: JSFiddle!

Answer 1

You could make use of CSS3 animations. I wrote some examplecode which shows a progressbar which counts down using a duration you can choose. You can also have a callback when the animation is finished.

CSS3 animations are hardware-accelerated, so you'll have the smoothest experience when you make use of it.

/*
 *  Creates a progressbar.
 *  @param id the id of the div we want to transform in a progressbar
 *  @param duration the duration of the timer example: '10s'
 *  @param callback, optional function which is called when the progressbar reaches 0.
 */
function createProgressbar(id, duration, callback) {
  // We select the div that we want to turn into a progressbar
  var progressbar = document.getElementById(id);
  progressbar.className = 'progressbar';

  // We create the div that changes width to show progress
  var progressbarinner = document.createElement('div');
  progressbarinner.className = 'inner';

  // Now we set the animation parameters
  progressbarinner.style.animationDuration = duration;

  // Eventually couple a callback
  if (typeof(callback) === 'function') {
    progressbarinner.addEventListener('animationend', callback);
  }

  // Append the progressbar to the main progressbardiv
  progressbar.appendChild(progressbarinner);

  // When everything is set up we start the animation
  progressbarinner.style.animationPlayState = 'running';
}

addEventListener('load', function() {
  createProgressbar('progressbar1', '40s');
  createProgressbar('progressbar2', '30s');
  createProgressbar('progressbar3', '20s', function() {
    alert('20s progressbar is finished!');
  });
  createProgressbar('progressbar4', '10s', function() {
    alert('10s progressbar is finished!');
  });
});

.progressbar {
  width: 80%;
  margin: 25px auto;
  border: solid 1px #000;
}
.progressbar .inner {
  height: 15px;
  animation: progressbar-countdown;
  /* Placeholder, this will be updated using javascript */
  animation-duration: 40s;
  /* We stop in the end */
  animation-iteration-count: 1;
  /* Stay on pause when the animation is finished finished */
  animation-fill-mode: forwards;
  /* We start paused, we start the animation using javascript */
  animation-play-state: paused;
  /* We want a linear animation, ease-out is standard */
  animation-timing-function: linear;
}
@keyframes progressbar-countdown {
  0% {
    width: 100%;
    background: #0F0;
  }
  100% {
    width: 0%;
    background: #F00;
  }
}

<div id='progressbar1'></div>
<div id='progressbar2'></div>
<div id='progressbar3'></div>
<div id='progressbar4'></div>