Get elapsed time, time ago, supports timezone

kli-js-elapsed-time.js

/**
 * Get elapsed time, time ago, supports timezone
 * @param  integer time --- string | unix timestamp
 * @param  strings --- string | array
 * @return string elapsed time
 */
function(datetime, strings, elative_to) {

	if (arguments.length) {
		var datetime = typeof datetime !== 'string' ? datetime : new Date(datetime)
	} else {
		var datetime = new Date()
	}

	if (Object.prototype.toString.call(strings) !== '[object Array]' || strings.length !== 7) {
		if (typeof strings == 'string' && strings == 'short') {
			var strings = [
				'<1m',
				'~1m',
				'm',
				'~1h',
				'h',
				'~1d',
				'd'
			]
		} else {
			var strings = [
				'Less than a minute ago',
				'About a minute ago',
				' minutes ago',
				'About an hour ago',
				' hours ago',
				'1 day ago',
				' days ago'
			]
		}
	}

	var relative_to = typeof relative_to == 'undefined' || !relative_to ? new Date() : new Date(relative_to)
	var delta = parseInt((relative_to.getTime() - datetime) / 1000);
	delta = delta + (relative_to.getTimezoneOffset() * 60);

	if (delta < 60) {
		return strings[0];
	} else if (delta < 120) {
		return strings[1];
	} else if (delta < (60 * 60)) {
		return (parseInt(delta / 60)).toString() + strings[2];
	} else if (delta < (120 * 60)) {
		return strings[3];
	} else if (delta < (24 * 60 * 60)) {
		return 'About ' + (parseInt(delta / 3600)).toString() + strings[4];
	} else if (delta < (48 * 60 * 60)) {
		return strings[5];
	} else {
		return (parseInt(delta / 86400)).toString() + strings[6];
	}
}