# nom-ts TypeScript helpers for nominal typing --- # Problem - 😀 Nominal types are [pretty useful](https://github.com/Microsoft/TypeScript/blob/69abe49930761aea92dc564f9b6a5db74d6e1be9/src/compiler/types.ts#L1183-L1192). - 😞 TypeScript doesn't support nominal types ([yet?](https://github.com/microsoft/TypeScript/wiki/Roadmap/69ede9ef95de7bf8764a2f2fa3c3d4c441cc828d#future)). Great! This is easy to fix right? The simple trick below solves the problem. ```ts declare const __brand: unique symbol; declare const __type: unique symbol; interface __Brand { [__brand]: S; [__type]: T; } export type Brand = T & __Brand; ``` But then we encounter some more happy little problems. ```ts type PlayerId = Brand; type PlayerScores = Record; const myId = 1337 as PlayerId; const scores: PlayerScores = { [myId]: 9001 }; // Element implicitly has an 'any' type because expression // of type 'Brand' can't be used to // index type 'Record, number>'. // ts(7053) const myScore = scores[myId]; ``` **nom-ts aims to address these problems.** # Goals - 🦅 no dependencies - 🦥 all branded types in nom-ts are assignable to their underlying type without any additional syntax # The rest of the code ```ts interface __Flavor { [__brand]?: S; /** * Intersection is distributive over union, but we don't want to "lose" information about T. * `__type?: T` will be useful for Unbrand. */ [__type]?: T; } export type Flavor = T & __Flavor; export type Unbrand = T extends Flavor ? X : T; export const Unbrand = (x: T) => x as Unbrand; export type Dict = Record, V>; ``` # Links - https://github.com/Microsoft/TypeScript/issues/202 - https://basarat.gitbooks.io/typescript/docs/tips/nominalTyping.html - "Brand" name is taken from https://michalzalecki.com/nominal-typing-in-typescript/ - "Flavor" name is taken from https://spin.atomicobject.com/2018/01/15/typescript-flexible-nominal-typing/ - https://github.com/gcanti/newtype-ts ---- #### Credits This project was bootstrapped with [TSDX](https://github.com/jaredpalmer/tsdx).

nom-ts

Downloads in past1 Month3 Months6 Months1 Year2 Years5 YearsAll time

Stats

Sick of boring JavaScript newsletters?

Downloads in past