type-fest VS nominal

Related: https://github.com/sindresorhus/type-fest/blob/main/source/o...

Typescript doesn’t natively provide an Opaque type that we can use to define a string that has already been localized. If the data looks like a string, Typescript will consider it a string. We can however use utility types that simulate opaque types, like the Opaque definition in type-fest:

With these powerful features, you can create dynamic and expressive types. One last thing I want to mention before moving on, is that you can install libraries with which you can add more types to your project like type-fest or utility-types. These libraries contain a lot of useful types that you can use in your project.

Also, it’s not as restrictive as mutability tools — if you know what you are doing and want to ignore this limitation for a particular case, you can apply the -readonly modifier or the Writeable type from type-fest or ts-essentials.

Remember you can derive one type from another type so you can make sure they don't diverge. SetOptional type util

Some folks have built whole SQL databases and DSL compilers in the TS type system. These tend to be toy projects with disclaimers not to use them. But the type system being Turing complete[0] (for better or worse), pretty much whatever you can imagine. This project[1] is one I actually return to frequently for practical ideas.

0: https://github.com/microsoft/TypeScript/issues/14833

1: https://github.com/sindresorhus/type-fest

Have a look at SetRequired and SetOptional in type-fest

Try the Exact method provided by Type Fest, looks like it does what you're looking for

This is a fairly common scenario and available via libraries like type-fest or implementable with a couple lines of code.

Hey OP here, Wanted to share something we recently discovered in typescript. This is a way to to create haskell style Newtype using the lesser known \`symbols\` ```ts type Minutes = number type Seconds = number const minutesToSeconds = (minutes: Minutes) => minutes * 60 const seconds: Seconds = 420 // uh-oh, we can use Minutes and Seconds interchangeably minutesToSeconds(seconds) ``` Nominal types solve this problem ```ts import { Nominal, nominal } from 'nominal-types'; type Minutes = Nominal<'Minutes', number>; type Seconds = Nominal<'Seconds', number>; const minutesToSeconds = (minutes: Minutes) => minutes * 60 // You can directly type cast or use nominal.make const seconds = nominal.make(420) const minutes = 1337 as Minutes // doesn't work, yay type safety minutesToSeconds(seconds) // does work! minutesToSeconds(minutes) ``` We have some lot cooler examples https://github.com/modfy/nominal#examples You can also read more about it here: https://zackoverflow.dev/writing/nominal-and-refinement-types-typescript