alarm.html

<audio id="alarm" src="alarm.ogg" controls></audio>
<script>
 const alarmElement = document.getElementById('alarm');
 const alarmTimes = [
   new Date('2015-11-13 07:00 -0500'),
   new Date('2015-11-13 08:00 -0500'),
   new Date('2015-11-13 08:30 -0500'),
 ];

 function playAlarm() {
   alarmElement.currentTime = 0;
   alarmElement.play();
 }

 function checkTime(time) {
   if (Date.now() >= time) {
     return playAlarm();
   }

   const diff = time - Date.now();
   console.log('%s seconds until alarm', diff/1000|0);
   setTimeout(playAlarm, diff);
 }

 function stopAlarm() {
   alarmElement.pause();
 }

 alarmTimes.forEach(time => checkTime(time));
 document.body.addEventListener('keypress', e => {
   // Spacebar 
   if (e.keyCode == 32) {
     stopAlarm()
   }
 });
 </script>

I learnt two little tricks :D

1. double | 0 -> convert to integer
2. date2 - date1 -> diff in ms

Thanks 👍