Create a countdown timer in Dart

index.html

<div>
  <strong id="days"></strong> 
  <strong id="hours"></strong> 
  <strong id="minutes"></strong> 
  <strong id="seconds"></strong>
</div>

main.dart

void main() {
  var christmas2019 = DateTime(2019, 12, 25);
  
  Timer.periodic(Duration(seconds: 1), (_) {
  	var now = DateTime.now();
    var diff = christmas2019.difference(now);
    var inMilli = diff.inMilliseconds;
    var inSeconds = diff.inSeconds;

    var seconds = (inSeconds % 60).floor();
    var minutes = ((inSeconds / 60) % 60).floor();
    var hours = ((inMilli / (1000 * 60 * 60)) % 24).floor();
    var days = (inMilli / (1000 * 60 * 60 * 24)).floor();

    querySelector('#days').innerHtml = '${days}d';
    querySelector('#hours').innerHtml = '${hours}h';
    querySelector('#minutes').innerHtml = '${minutes}m';
    querySelector('#seconds').innerHtml = '${seconds}s';
  });
}

See this in action: https://dartpad.dartlang.org/0d0d8cb8452af0f30cdf98d506053f7c