@bybrave/fast-deep-equal2

Maintained, drop-in fork of fast-deep-equal — the fastest deep-equality check for JavaScript.

The original has had no release since 2020 (3.1.3) while still pulling ~710M downloads/month. This fork fixes the null-prototype crash, adds a circular-safe variant, folds Map/Set/TypedArray support into the default function, and ships ESM plus improved bundled types.

npm install @bybrave/fast-deep-equal2

const equal = require('@bybrave/fast-deep-equal2');   // CommonJS
import equal from '@bybrave/fast-deep-equal2';         // ESM
import { equal, react, circular } from '@bybrave/fast-deep-equal2';

equal({ a: 1, b: [2, 3] }, { a: 1, b: [2, 3] }); // true

The default equal(a, b) is the same fast function as upstream, and remains a TypeScript type guard (a is T). Map, Set, TypedArray and BigInt are compared out of the box — no separate es6 entry needed.

What's fixed

| Issue | Problem | Fix | |---|---|---| | #49 / #111 | Comparing objects created with Object.create(null) threw a.valueOf is not a function (21+ 👍). | valueOf/toString are only called when the object actually overrides them and they're callable — null-prototype objects compare by their own keys instead. | | #17 | Circular references caused a RangeError (stack overflow). | New circular export tracks visited pairs and handles cycles. The default equal stays allocation-free and fast. | | #81 | Type fixes weren't shipped. | Bundled, improved types (default + react + circular), verified with tsc --strict. | | — | Map/Set/TypedArray lived in a separate es6 entry. | Folded into the default function (Node 18+ has them). |

Exports

• equal(a, b) (default) — fast deep equality, Map/Set/TypedArray/BigInt aware, null-prototype safe. Throws on circular references (use circular for those).
• circular(a, b) — same, but safe against circular references (tracks visited object pairs; slightly slower).
• react(a, b) — ignores React elements' circular _owner. Also available as the subpath @bybrave/fast-deep-equal2/react for drop-in parity with fast-deep-equal/react.

Migration from fast-deep-equal

Replace the dependency and the import. equal behaves the same, except comparing Object.create(null) objects now works instead of throwing. If you imported fast-deep-equal/es6, just use the default — Map/Set/TypedArray are built in. fast-deep-equal/react → @bybrave/fast-deep-equal2/react.

Support

If this package saves you time, you can support maintenance:

Bitcoin (BTC): bc1q37557q5jpeaxqydzwvf3jgj7zhnfpn2td3q40q

Credits & license

MIT, same as the original — see LICENSE. Based on fast-deep-equal by Evgeny Poberezkin.