JarCastingDuration 
This is a library for dealing with durations. It works well with javascript's Date objects.
$ npm install @icholy/duration
import Duration from "@icholy/duration";
Parse
ms- milliseconds- secondm- minuteh- hourd- dayw- week
var d = new Duration("6w5d4h3m2s1ms");
console.log(
d.milliseconds(), "\n", // => 4075382001
d.seconds(), "\n", // => 4075382
d.minutes(), "\n", // => 67923
d.hours(), "\n", // => 1132
d.days(), "\n", // => 47
d.weeks(), "\n" // => 6
);
Format
console.log(
"str:", Duration.hour.toString(),
"ms:", Duration.hour.valueOf()
); // => "str: 1h ms: 3600000"
Basic Operations
// Addition
var d1 = new Duration("6d"),
d2 = new Duration(d1 + Duration.day);
console.log(d2.toString()) // => "168h"
// Multiplication
var d3 = new Duration("5m"),
d4 = new Duration(d3 * 12);
console.log(d4.toString()) // => "1h"
// etc ...
Dates
// Adding duration to date
var d = Duration.parse("5h"),
now = new Date(),
later = new Date(now + d);
console.log(later.toString());
// Duration between two dates
var bday = new Date("March 3, 1991"),
now = new Date(),
age = new Duration(now - bday);
console.log(age.toString());
setTimeout / setInterval
setTimeout(function () {
// runs 5 minutes later
}, new Duration("5m"));
setInterval(function () {
// runs every 10 seconds
}, 10 * Duration.second);