is-kit Docs — TypeScript Type Guard Toolkit

Keep runtime checks aligned with your existing TypeScript object types.
Refine values, validate exhaustive unions, and safely handle unknown input.

Installation

pnpm add is-kit

Usage

import {
  and,
  isNumber,
  isString,
  not,
  or,
  predicateToRefine
} from 'is-kit';

const isShort = predicateToRefine<string>((s) => s.length <= 3);
const isShortString = and(isString, isShort);

isShortString('ok'); // true
isShortString('toolong'); // false
or(isString, isNumber)('x'); // true
not(isString)(42); // true

Features

Existing types

Build runtime guards around the TypeScript object types you already have. typedStruct<T>() helps keep runtime validation aligned when those types change.

API Reference

define

Wrap a predicate as a typed guard.

struct

Shape guard for objects; supports exact key checking.

logic

Logical combinators: and, andAll, or, not, guardIn.

parse

Guard values or decode and validate JSON with tagged results.

primitive

Primitive guards: string, number, boolean, nullish, etc.

predicate

Convert boolean predicates to refinements.

Read full TypeDoc reference