Time as a dependency in JavaScript/TypeScript — inspired by .NET TimeProvider

[jaenyf]

🏷️ Discussion Type

Product Feedback

Body

I've been working on an open-source TypeScript library called Time-Provider:

https://github.com/jaenyf/time-provider

The idea started from a fairly simple observation:

Time is a dependency.

.NET has treated it as such since .NET 8 with TimeProvider, but I felt the JavaScript/TypeScript/Node.js ecosystem was missing a similar abstraction.

That's why I created Time-Provider.

It doesn't just mimic .NET's TimeProvider. It goes a step further to fit the JavaScript ecosystem, where applications can use many different date/time libraries — Temporal, native Date, Day.js, Luxon, Moment, and others.

You can choose the date library that fits your stack while keeping everything type-safe.

The architecture is also extensible because not every environment provides the same APIs. For example, the Animation Frame API is available in browsers but not in Node.js, so it shouldn't necessarily be part of every runtime's baseline.

The goal is to make time something you can inject, rather than something you have to monkey-patch in your tests.

In my opinion, this leads to a cleaner design and fits well with Dependency Injection and DDD principles.

As of writing, time-provider provides an application with a single time interface containing:

• 🕐 a clock
• 📅 a date converter
• ⏱️ a scheduler, including timers
• 📈 a timings performance API

The same interface can then be backed by different clock strategies:

• System — real time for production
• Fixed — always the same instant
• Manual — advance time explicitly
• Sequential — return a predefined sequence of instants

For example, a test can create a manual clock:

const timeProvider = createTimeProvider
  .for(yourPreferredDatePlugin)
  .asManual()
  .withInitialTime("2026-01-01T00:00:00.000Z")
  .create();

let retries = 0;

timeProvider.scheduler.timers.every({ minutes: 1 }, () => retries++);

timeProvider.clock.moveBy({ seconds: 3 });

// retries === 3

Conceptually, this provides the same kind of deterministic control you get from Sinon/Jest fake timers, but with a narrower and more explicit scope.

No global monkey-patching, no waiting for real time to pass, and no need to couple your application to a particular testing framework.

Another important goal was not forcing applications to adopt a particular date library.

The project currently provides adapters for:

• Native Date
• Day.js
• Luxon
• Moment
• Moment Timezone
• Temporal

So you can keep your existing stack while still injecting time in a type-safe way.

The project is also designed around:

• 🌳 tree-shaking
• 📦 zero runtime dependencies in the core package
• 🔀 explicit production and deterministic runtimes
• 🔌 an extensible adapter architecture

I'd really like to get feedback from people who have dealt with time-dependent code and testing.

How do you currently handle time in your applications?

Do you prefer fake timers, dependency injection, clock abstractions, or something else?

Repository: https://github.com/jaenyf/time-provider

I'd especially appreciate feedback on the API design and whether this approach solves a problem you actually encounter.

Take care!

— Jaenyf

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[jaenyf]

The library was updated to v4.1.0 with a cleaner and netter API.
It supports disposable or abortable timers and mostly offers the same functionality as jest/sinon in a more readable manner.
Check it out on NPM or test it on its playground.