dateformat.js

var startTime = new Date();

function dateFormat(timestamp, currentDateFormat, timeSinceFormat) {

	// Format string timestamps to enforce a number unless it's not passed
	// as a human readable format. Ex: '1484897633537'.
	timestamp = isNaN(Number(timestamp)) ? timestamp : Number(timestamp);

	// Month and weekdays
	let listMonths 	= ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'],
		weekdays 	= ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];

	let nowDate 		= new Date(), // will be used to get the elapsed time
		timestampDate 	= new Date(timestamp);

	/*
	 * @method removeLeadingZero
	 * Removes the leading 0 of a number.  Ex (01 to 1, 05 to 5)
	 * @param num {number} - The number to be converted
	 * @returns {number} The converted number
	 */
	let removeLeadingZero = function(num) {
	  num = '' + num;
	  return (num.indexOf('0') == 0 && num != '0') ? num.substring(1) : num;
	}

	/*
	 * @method addLeadingZero
	 * Adds the leading 0 to a number that only has one digit.  Ex (1 to 01, 5 to 05)
	 * @param num {number} - The number to be converted
	 * @returns {number} The converted number
	 */
	let addLeadingZero = function(num) {
	  num = Number(num);
	  return isNaN(num) ? '00' : (((num < 10) ? '0' : '') + num);
	}

	/*
	 * @method getAMPM
	 * @param hours {number} - The timestamp hour
	 * @returns {string} the AM/PM according to the hour
	 */
	let getAMPM = function(hours) {
		if (Number(hours) > 11) {
			return 'PM';
		}
		return 'AM';
	}


	/*
	 * @method getOrdinal
	 * @param num {number} - the number to calculate the ordinal (st, nd, rd, th)
	 * @returns {string} the ordinal
	 */
	let getOrdinal = function(num) {
		if (num>3 && num<21) return 'th';
		switch (num % 10) {
			case 1:  return "st";
			case 2:  return "nd";
			case 3:  return "rd";
			default: return "th";
		}
	}

	/*
	 * @method convert24HoursIn12
	 * @param hours {number} - The timestamp hour
	 * @returns {number} The hour converted in 12 hour format
	 */
	let convert24HoursIn12 = function(hours) {

		let convertedHour = hours;

		if (hours == 0) {
			convertedHour = 12;
		}

		if (hours > 12) {
			convertedHour = hours - 12;
		}

		return convertedHour;
	}

	/*
	 * @method getElapsedMin
	 * @returns {number} Get the elapsed number of minutes passed from the timestamp to now
	 */
	let getElapsedMin = function() {
		return Math.floor((nowDate - timestampDate) / 1000 / 60);
	}

	/*
	 * @method getElapsedMin
	 * @returns {number} Get the elapsed number of hours passed from the timestamp to now
	 */
	let getElapsedHours = function() {
		return Math.floor((nowDate - timestampDate) / 1000 / 60 / 60);
	}


	/*
	 * @method convert24HoursIn12
	 * @param hours {number} - The timestamp hour
	 * @returns {number} The hour converted in 12 hour format
	 */
	let getElapsedTime = function() {

		let elapsedHours = getElapsedHours(),
			elapsedMin = getElapsedMin(),
			elapsedTime;

		// Format the elapsed time (X m ago or X h ago)
		if (elapsedHours < 1) {
			elapsedTime = removeLeadingZero(elapsedMin) + 'm ago';
		} else {
			elapsedTime = removeLeadingZero(elapsedHours) + 'h ago';
		}

		return elapsedTime;
	}


	/*
	 * @method constructDateParts
	 * Creates an object with all the parts of the time in order to make the format replacement
	 * @param timestampDate {Date} - The timestamp date to be formated
	 * @returns {Object}
	 */
	 let constructDateParts = function(timestampDate) {

		let hours = timestampDate.getHours(),
			date = timestampDate.getDate(),
			minutes = timestampDate.getMinutes();

	 	return {
			month: addLeadingZero(timestampDate.getMonth() + 1),
			date: addLeadingZero(date),
			dateOneDigit: removeLeadingZero(date),
			year: addLeadingZero(timestampDate.getFullYear()),
			ampm: getAMPM(hours),
			day: timestampDate.getDay(),
			hour24: addLeadingZero(hours),
			hour24OneDigit: removeLeadingZero(hours),
			hour12: addLeadingZero(convert24HoursIn12(hours)),
			hour12OneDigit: removeLeadingZero(convert24HoursIn12(hours)),
			minutes: addLeadingZero(minutes),
			minutesOneDigit: removeLeadingZero(minutes),
			ordinal: getOrdinal(date),
			elapsedHour: getElapsedHours(),
			elapsedTime: getElapsedTime()
		};

	 }

	/*
	 * @method datePatternReplace
	 * Replaces the strings looking for the matching date formats and replace them with value based on the timestamp
	 * @param dateFromatStr {string} - The string to be formatted. Ex: HH:ii - DD:MM
	 * @returns {string} The formated string with the date format replacements
	 */
	let datePatternReplace = function(dateFromatStr) {

		let weekDay 		= weekdays[dateParts.day], // Tuesday
			weekDayMid 		= weekDay.substring(0, 3), // Tue
			weekDayShort 	= weekDay.substring(0, 2), // Tu
			monthLong 		= listMonths[Number(dateParts.month) - 1], // June
			monthShort 		= monthLong.substring(0, 3), // Jun
			yearShort 		= dateParts.year.substring(2), // 17 (2017)
			amPmLowercase 	= dateParts.ampm.toLowerCase(); // am/pm

		// Execute the replacement and format the date/time
		dateFromatStr = dateFromatStr
					// AM/PM - am/pm
					.replace(/AA/g, dateParts.ampm)
					.replace(/aa/g, amPmLowercase)

					// Hours (24)
					.replace(/HH/g, dateParts.hour24)
					.replace(/H/g, dateParts.hour24OneDigit)

					// Hours (12)
					.replace(/hh/g, dateParts.hour12)
					.replace(/h/g, dateParts.hour12OneDigit)

					// Minutes
					.replace(/II/g, dateParts.minutes)
					.replace(/I/g, dateParts.minutesOneDigit)

					// Date
					.replace(/DD/g, dateParts.date)
					.replace(/D/g, dateParts.dateOneDigit)

					// Ordinal for date
					.replace(/O/g, dateParts.ordinal)

					// Year
					.replace(/YYYY/g, dateParts.year)
					.replace(/YY/g, yearShort)

					// Elapsed time (Hours and Minutes)
					.replace(/GG/g, dateParts.elapsedTime)

					// Month
					.replace(/MM/g, monthLong)
					.replace(/M/g, monthShort)

					// Week day
					.replace(/EEEE/g, weekDay)
					.replace(/EEE/g, weekDayMid)
					.replace(/EE/g, weekDayShort);

		return dateFromatStr;
	}

	// Get the object with date formats
	let dateParts = constructDateParts(timestampDate)

	// Get the formatted string based on the elapsed
	let formatedString = '';

	// If the elapsedHours is within 24 hours and the timeSinceFormat is defined
	if (dateParts.elapsedHours < 24 && timeSinceFormat) {
		formatedString = datePatternReplace(timeSinceFormat);
	} else {
		formatedString = datePatternReplace(currentDateFormat);
	}

	return formatedString;

}

//let t = 'Fri Jan 24 2017 13:50:28 GMT+1100 (AEDT)';
let t = '1484897633537';

console.log(dateFormat(t, 'DD M', 'GG'));
console.log(dateFormat(t, 'EEE, DD M'));
console.log(dateFormat(t, 'DDO M YY HH:II'));
console.log(dateFormat(t, 'h:Iaa'));
console.log(dateFormat(t, 'GG'));

/*
	AA - AM/PM
	aa - am/pm
	HH - hours (24) - 2 digits
	H - hours (24) - 1 digit
	hh - hours (12) - 2 digits
	h - hours (12) - 1 digit
	II - minutes - 2 digits
	I - minutes - 1 digit
	DD - date - 2 digits
	D - date - 1 digit
	O - date - ordinal
	MM - month - Long name
	M - month - Short name
	EEEE - week - long name
	EEE - week - 3 letters name
	EE - week - 2 letters name
	YYYY - year - Long
	YY - year - Short
	GG - elapse min/hours
*/


// later record end time
var endTime = new Date();

// time difference in ms
var timeDiff = endTime - startTime;
timeDiff /= 1000;

console.log(timeDiff);