Rare find

Is. A tool that checks what type of data you're working with.

github.com/sindresorhus/is

Problem

The full read on this project is a sign-in away — what it solves, who it serves, and where it sits in the market.

Audience

The full read on this project is a sign-in away — what it solves, who it serves, and where it sits in the market.

Market

The full read on this project is a sign-in away — what it solves, who it serves, and where it sits in the market.

Pricing

The full read on this project is a sign-in away — what it solves, who it serves, and where it sits in the market.

Vaya's read on this project

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Updates

May 2026

Fix CI May 11
Release — May 11
8.1.0 May 11
Add negative assertion helper May 11

April 2026

Release — Apr 9
8.0.0 Apr 9
Fix some type guards Apr 9
Fix `isEnumCase` incorrectly accepting numeric enum key names Apr 9
Add `negativeInteger`, `nonNegativeInteger`, `arrayOf`, and `oneOf` p… Apr 8
Add `finiteNumber`, `nonNegativeNumber`, and `positiveInteger` predic… Apr 8
Fix `isInRange` silently returning false when range contains `NaN` Apr 8
Fix `isNumericString` incorrectly accepting strings with surrounding … Apr 7
Fix handling of functions and arrays in `isEmptyObject` and `isNonEmp… Apr 7
Require Node.js 22 Apr 7

December 2025

Release — Dec 27
7.2.0 Dec 27
Add predicate factory mode to `is.any` and `is.all` Dec 27

October 2025

Release — Oct 31
7.1.1 Oct 31
Fix `is.class` for minified class expression (#217) Oct 31

September 2025

Release — Sep 13
7.1.0 Sep 13
Add `is.optional` and `assert.optional` Sep 13
Fix TypeScript type narrowing issue with `isUrlString` Sep 11

June 2025

Structure fixtures so they can be easily tested for exclusivity (#215) Jun 6
Release — Jun 4

September 2024

Release — Sep 6

July 2024

Release — Jul 10

May 2024

Release — May 16

April 2024

Release — Apr 23