Show HN: Is-Kit – Lightweight TypeScript Guard and Validator Toolkit

1 month ago 2

Lightweight, zero-dependency toolkit for building isFoo style type guards in TypeScript. Runtime-safe 🛡️, composable 🧩, and ergonomic ✨.

👉 See full document

Tired of writing the same isFoo again and again? Let is-kit do it for you:

Less boilerplate
Type-safe
Composable
Zero-dependency

☕ Grab a coffee, let is-kit do the boring work.

Node via npm

pnpm add is-kit # or bun add is-kit # or npm i is-kit # or yarn add is-kit

ESM and CJS builds are provided for npm consumers. Types are bundled.

// Deno/Bun/JSR-aware tooling import { define, and, or } from 'jsr:@nyaomaru/is-kit';

Build is functions from tiny, composable pieces:

import { define, predicateToRefine, and, or, not, isString, isNumber, } from 'is-kit'; // 1. define small pieces const isShortString = define<string>( (value) => isString(value) && value.length <= 3 ); const isPositive = predicateToRefine<number>((num) => num > 0); // 2. compose them const isPositiveNumber = and(isNumber, isPositive); const shortOrPositive = or(isShortString, isPositiveNumber); const isOther = not(shortOrPositive); // 3. use them shortOrPositive('foo'); // true shortOrPositive(42); // true isOther(false); // true

These primitives plug into higher-level combinators like struct when you need to shape objects.