A utility package for JavaScript applications.
Local drop-in replacement services for CI and no-network sandboxes
Lightweight, dependency free, fast, customizable datepicker written in pure JavaScript. 
Solves a problem with util.format
The assert module from Node.js, for the browser.
minimalistic-assert ===
Parses, serializes, and manipulates MIME types, according to the WHATWG MIME Sniffing Standard
uvu is an extremely fast and lightweight test runner for Node.js and the browser
Synchronous validation of a path existing either as a file or as a directory.
correct invalid SPDX expressions
assert with status codes
A robust, ES3 compatible, "has own property" predicate.
Extra assertions on top of node's assert module
Fastest deep equal comparison for React. Great for React.memo & shouldComponentUpdate. Also really fast general-purpose deep comparison.
Is this value a JS SharedArrayBuffer?
Is this value a JS ArrayBuffer?
Which kind of boxed JS primitive is this?
Node.js globbing for amqp-like topics
Various utility functions
What is the type of this builtin JS value?
Is this value a JS Typed Array? This module works cross-realm/iframe, does not depend on `instanceof` or mutable properties, and despite ES6 Symbol.toStringTag.
Is this specifier a node.js core module?
`Object.getOwnPropertyDescriptor`, but accounts for IE's broken implementation.
`Object.defineProperty`, but not IE 8's broken one.