3 examples of 'age calculation using jquery datepicker' in JavaScript

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function calculateAge(el) {
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  return 2016 - el;
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}

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export function ageAsOf(birthDate, date) {
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  if (!birthDate || !date || !birthDate.isValid() || !date.isValid()) {
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    return null;
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  }
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  const onOrAfterBirthday = (
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    date.month() > birthDate.month() || (
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      date.month() === birthDate.month()
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      && date.date() >= birthDate.date()
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    )
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  );
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  return (date.year() - birthDate.year() - (onOrAfterBirthday ? 0 : 1));
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}

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function calcAges() {
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			var HOUR = 60 * 60 * 1000;
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			var DAY = HOUR * 24;
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			var WEEK = DAY * 7;
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			var MONTH = DAY * 30;
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			var YEAR = DAY * 365;
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            var elts = document.getElementsByTagName("time");
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			var elt;
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			for (var i = 0; elt = elts[i]; i++) {
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				elt.title = elt.textContent || elt.innerHTML;
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				var iso = elt.getAttribute("datetime");
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				var date = new Date(iso);
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				var now = new Date();
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				var diff = now.getTime() - date.getTime();
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				var str = elt.innerHTML;
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				if (diff > YEAR) str = toAge(diff / YEAR, "năm");
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				else if (diff > MONTH) str = toAge(diff / MONTH, "tháng");
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				else if (diff > WEEK) str = toAge(diff / WEEK, "tuần", true);
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				else if (diff > DAY) str = toAge(diff / DAY, "ngày", true);
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				else if (diff > HOUR) str = toAge(diff / HOUR, "tiếng", true);
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				else str = "Mới bây giờ";
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				elt.innerHTML = str;
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			}
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		}