code: function timeElapsed(timeStamp) {
  		var diff = _timeDifference(timeStamp);
  		var yearStr = _generateTimeString(diff.year, "a year", "years");
  		var monthStr = _generateTimeString(diff.month, "a month", "months");
  		var dayStr = _generateTimeString(diff.day, "a day", "days");
  		var hourStr = _generateTimeString(diff.hour, "an hour", "hours");
  		var minuteStr = _generateTimeString(diff.minute, "a minute", "minutes");
  		var disPlayStr = "";
  		if(yearStr) {
  			disPlayStr = diff.year > 0 ? yearStr : yearStr + monthStr;
  		} else if(monthStr) {
  			disPlayStr = diff.month > 0 ? monthStr : monthStr + dayStr;
  		} else if(dayStr) {
  			disPlayStr = diff.day > 0 ? dayStr : dayStr + hourStr;
  		} else if(hourStr) {
  			disPlayStr = diff.hour > 0 ? hourStr : hourStr + minuteStr;
  		} else if(minuteStr) {
  			disPlayStr = minuteStr;
  		}
  		return disPlayStr;	
  	}
docs: Returns the time duration passed by now. E.g. "2 minutes", "an hour", "a day", "3 months", "2 years"
  @param {String} timeStamp
  @returns {String} If the duration is less than 1 minute, it returns empty string "". Otherwise it returns a duration value.