function updateClock() {
   var currentTime = new Date();
   var currentHours = currentTime.getHours();
   var currentMinutes = currentTime.getMinutes();
   var currentSeconds = currentTime.getSeconds();
   // Pad the minutes and seconds with leading zeros, if required
   currentMinutes = (currentMinutes < 10 ? "0" : "") + currentMinutes;
   currentSeconds = (currentSeconds < 10 ? "0" : "") + currentSeconds;
   // Choose either "AM" or "PM" as appropriate
   var timeOfDay = (currentHours < 12) ? "AM" : "PM";
   // Convert the hours component to 12-hour format if needed
   currentHours = (currentHours > 12) ? currentHours - 12 : currentHours;
   // Convert an hours component of "0" to "12"
   currentHours = (currentHours == 0) ? 12 : currentHours;
   // Compose the string for display
   var currentTimeString = currentHours + ":" + currentMinutes + ":" + currentSeconds + " " + timeOfDay;
   document.querySelector('#clock').innerHTML = currentTimeString;
}
updateClock(); // To load the timer immediately
setInterval(updateClock, 1000); //To update it
<div id="clock"></div>