Typed Duration

!Node.js CI

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.

Note: requires TypeScript 3.8 or later

Version 1.x works on Node 10+
Version 2.x requires Node 16+

Installation

Install the library to your project:

``
npm i typed-duration
`

Use

Consider the following code:

`TypeScript
setTimeout(doSomething, 1000)
`

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

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

With this library, you can do this:

`TypeScript
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:

`TypeScript
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:

`TypeScript
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))
`

#winning

Backward-compatible API

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

`TypeScript
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)
`

Logging

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:

`TypeScript
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.