is-kit

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Type-safe utilities and combinators for building isXXX guards in TypeScript. Lightweight and zero-dependency.

Installation

pnpm add is-kit

Usage

import { define } from 'is-kit';


const isString = define<string>((x) => typeof x === 'string');


if (isString('hello')) {
  // narrowed to string
}

Features

Type-safe predicates

Author and compose predicates that refine types precisely.

API Reference

define
Wrap a predicate as a typed guard.
logic
Logical combinators: and, andAll, or, not, guardIn.
parse
Safe parsing with tagged results.
struct
Shape guard for objects; supports exact key checking.
arrayOf
Guard arrays with an element guard.
oneOf
Passes when any guard passes (union).
Read full TypeDoc reference