code:

function updateClock() {
  var days = ["SUNDAY","MONDAY","TUESDAY","WEDNESDAY","THURSDAY","FRIDAY","SATURDAY"];
  var months = ["JANUARY","FEBRUARY","MARCH","APRIL","MAY","JUNE","JULY","AUGUST","SEPTEMBER","OCTOBER","NOVEMBER","DECEMBER"];
  var dateSuffix = {1:"st",2:"nd",3:"rd",4:"th",5:"th",6:"th",7:"th",8:"th",9:"th",0:"th"};
  var timeSuffix;
  var m = new Date();

  if (m.getHours() < 12) timeSuffix = "AM" 
  else timeSuffix = "PM";

  dateString =
    (days[m.getDay()]) + " " +  
    ("0" + (m.getMonth()+1)).slice(-2) +"/"+
    ("0" + m.getDate()).slice(-2) + "/" +
    m.getFullYear() + " " +
    (("0" + m.getHours()).slice(-2) % 12) + ":" +
    ("0" + m.getMinutes()).slice(-2) + " " + timeSuffix;
    // Ex: "MONDAY 10/03/2016 15:13:27"

  dateStringLong = 
    "It's " + 
    (("0" + m.getHours()).slice(-2) % 12) + ":" +
    ("0" + m.getMinutes()).slice(-2) + " " + timeSuffix + " on " +
    (days[m.getDay()]).toLowerCase().capitalize() + ", " +
    (months[m.getMonth()]).toLowerCase().capitalize() + " " +
    m.getDate() + dateSuffix[("" + m.getDate()).slice(-1)] + ", " +
    m.getFullYear();
    // Ex: "It's 15:13 on Monday, October 3rd, 2016" 

  // set the content of the element with the ID time to the formatted string
  if (switchVal==0) document.getElementById('time').innerHTML = dateString;
  else if (switchVal==1) document.getElementById('time').innerHTML = dateStringLong;

  // call function again in 1s
  setTimeout(updateClock, 1000);
}
updateClock(); // initial call