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1.0.13 • Public • Published

Typed Duration

Node.js CI npm version

A Zero-dependency typed duration library for JavaScript/TypeScript. Express and convert time durations with type-safety.

This library uses Value Object Typing to allow you to express time durations in a type-safe way, and perform conversion between different units.


Install the library to your project:

npm i typed-duration


Consider the following code:

setTimeout(doSomething, 1000)

It's pretty clear that these are milliseconds, because you know the API. Typically, developers might do something like:

setTimeout(doSomething, 5 * 60 * 1000) // In Five Minutes

With this library, you can do this:

import { Duration } from 'typed-duration'
const { milliseconds, minutes } = Duration
const period = minutes.of(5)
setTimeout(doSomething, milliseconds.from(period)) // Every Five Minutes

Well, that looks like more code. Yes, it is. It is also more semantically expressive of the programmer's intent, which makes it better for maintenance.

The situation is exacerbated when you expose a programming API that takes a time duration as a number. We all know that setTimeout takes milliseconds, but how do you communicate to consumers of your API what the time units are for timeout in your API call?

You should, of course, document it, and put it in JSDoc comments so that they can get hinting in their IDE.

You could call it timeoutSeconds to make it clear that it expects seconds.

Or you could make it take a TimeDuration and allow them to pass in whatever they want, and convert it to the units you need, like this:

import { Duration, TimeDuration } from 'typed-duration'
function executeLater(fn: () => void, delay: TimeDuration) {
    setTimeout(fn, Duration.milliseconds.from(delay))

Now, consumers of this function can call it like this:

import { Duration } from 'typed-duration'
const { milliseconds, seconds, minutes, hours, days } = Duration
// After 2.5 seconds
executeLater(doSomething, milliseconds.of(2500))
// After 10 seconds
executeLater(doSomething, seconds.of(10))
// After 15 minutes
executeLater(doSomething, minutes.of(15))
// After 3 hours
executeLater(doSomething, hours.of(3))
// After 6 days
executeLater(doSomething, days.of(6))


Backward-compatible API

If you have an existing API you want to add this to, you can use the MaybeTimeDuration type, like this:

import { Duration, MaybeTimeDuration } from 'typed-duration'
function executeLater(fn: () => void, period: MaybeTimeDuration) {
    setTimeout(fn, Duration.milliseconds.from(period))
// You can pass in a typed duration, and it will convert to a number of milliseconds
executeLater(doSomething, Duration.seconds.from(20))
// a number will be allowed by the MaybeTimeDuration type
// and the milliseconds.from() call will simply pass it through
executeLater(doSomething, 2500)


You can log times for user information in the format that the user specified them, including units, with Duration.value.of. You can supply an optional default unit to be used for untyped numbers (if you don't, it will just print the number).

For example:

import { Duration, MaybeTimeDuration } from 'typed-duration'
function executeLater(fn: () => void, delay: MaybeTimeDuration) {
    console.log(`Executing in ${Duration.value.of(delay, "ms")}...`)
    setTimeout(fn, Duration.milliseconds.from(delay))
executeLater(doSomething, Duration.seconds.from(20))
// Executing in 20s...
executeLater(doSomething, Duration.milliseconds.from(350))
// Executing in 350ms...
executeLater(doSomething, Duration.hours.from(3))
// Executing in 3h...
executeLater(doSomething, 2500)
// Executing in 2500ms...

Feature Requests, Bug Reports

See the GitHub repo.


npm i typed-duration

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