@opentf/obj-diff

The Fast, Accurate, and Modern JavaScript Objects Diffing & Patching Library.

Documentation & Playground

---

🚀 Features

• 🔍 Deep Objects Diffing: Detects changes at any depth.
• ✂️ Compact Array Diffs: Shortest edit scripts (Myers LCS) — inserting one element into a 10k array yields 1 op, not 10,001.
• 🩹 Efficient Patching: Apply diffs to recreate target objects.
• 🧬 Type-Safe Serialization: Round-trip diffs across network/process boundaries with serialize and deserialize preserving all JS native types.
• 🛠️ Extensible: Support for custom object types via diffWith().
• 📦 Modern Ecosystem: Built for Bun, Node.js, Deno, and Browser.
• 🟦 TypeScript Native: Full type safety and autocompletion.
• ⚡ High Performance: Optimized for speed and minimal memory footprint.

📦 Installation

Install @opentf/obj-diff using your preferred package manager:

# Bun
bun add @opentf/obj-diff

# pnpm
pnpm add @opentf/obj-diff

# npm
npm install @opentf/obj-diff

# Deno
deno add @opentf/obj-diff

🛠 Supported Types

The library natively supports the following types:

• Primitives: Undefined, Null, Number, String, Boolean, BigInt.
• Built-in Objects: Plain Objects {}, Array, Date, Map, Set, TypedArray (Uint8Array, Float32Array, etc.), ArrayBuffer, DataView.
• Temporal: all Temporal types (Instant, PlainDate, PlainTime, PlainDateTime, PlainYearMonth, PlainMonthDay, ZonedDateTime, Duration) — compared as immutable values (Duration structurally by its canonical string, since it has no .equals()).
• Class Instances: instances sharing the same prototype are diffed by their own enumerable properties; instances of different classes are reported as replaced.

📖 Usage

diff(obj1, obj2)

Performs a deep comparison between two objects.

import { diff } from '@opentf/obj-diff';

const result = diff(obj1, obj2);

DiffResult Structure

type DiffResult = {
  type: 0 | 1 | 2 | 3 | 4; // 0: Deleted, 1: Added, 2: Changed,
                           // 3: Inserted (array splice-in), 4: Removed (array splice-out)
  path: Array<unknown>;    // path to the property; Map entries use the Map key itself
  value?: unknown;         // the new value (for types 1, 2 and 3)
};

Types 3 (INSERTED) and 4 (REMOVED) are array-only splice operations with application-time indexes — they are what make array diffs compact:

diff([1, 2, 3], [0, 1, 2, 3]);
//=> [{ type: 3, path: [0], value: 0 }]  // 1 op, not 4

The constants (DELETED, ADDED, CHANGED, INSERTED, REMOVED) are exported from the package root.

patch(obj, patches)

Applies an array of diff results to an object.

import { patch } from "@opentf/obj-diff";

const updatedObj = patch(originalObj, diffResults);

serialize(diff) / deserialize(wire)

A diff holds live values by reference, so JSON.stringify loses their types (Date→string, Map/Set→{}, BigInt→throws). Use serialize/deserialize to send a diff across a process or network boundary and patch it back into the correct types on the other side:

import { diff, patch, serialize, deserialize } from "@opentf/obj-diff";

// client
const wire = serialize(diff(a, b)); // a JSON string, type-safe

// server
const patched = patch(a, deserialize(wire)); // Date/Map/Set/… restored exactly

value stays readable — each special value becomes a reference token "@n", with the real types collected in a per-op $refs table:

{
  "type": 1,
  "path": ["user"],
  "value": { "id": 1, "lastSeen": "@1", "roles": "@2" },
  "$refs": {
    "1": { "_t": "Date", "_v": "2026-07-15T00:00:00.000Z" },
    "2": { "_t": "Set", "_v": ["admin", "editor"] }
  }
}

Every supported type is preserved (Date, RegExp, Map, Set, TypedArray, ArrayBuffer, DataView, Error, URL, BigInt, Temporal, …), nested to any depth. Circular references and objects shared by identity are rebuilt with the same identity on the far side (plain objects and arrays are hoisted into $refs when referenced more than once; single-use containers stay inline). Symbols, functions, class instances, and cycles that run through a Map/Set/Error throw. Deserializing a Temporal value requires a Temporal implementation on globalThis.

stringify(value) / parse(wire)

Need the same type-safe codec for any value, not just a diff? stringify/parse are the general-purpose counterpart — a drop-in, richer JSON.stringify/JSON.parse that keeps native types intact:

import { stringify, parse } from "@opentf/obj-diff";

const wire = stringify({
  when: new Date(),
  tags: new Set(["a", "b"]),
  prefs: new Map([["theme", "dark"]]),
  big: 42n,
});

const value = parse(wire); // Date / Set / Map / BigInt all restored

Same coverage as above — every native type, plus circular references and shared identity. Symbols, functions, and class instances throw.

---

💡 Examples

1. Basic Objects

const a = { a: 1, b: 2 };
const b = { a: 2, c: 3 };

diff(a, b);
/*
[
  { type: 2, path: ["a"], value: 2 },
  { type: 0, path: ["b"] },
  { type: 1, path: ["c"], value: 3 }
]
*/

2. Nested Structures

const a = { foo: { bar: [1, 2] } };
const b = { foo: { bar: [1] } };

const d = diff(a, b);
const res = patch(a, d); // res is deep equal to b

3. ES6 Map & Set Support

Natively diff and patch modern collections.

const a = new Set([1, 2]);
const b = new Set([2, 3]);

diff(a, b);
/*
[
  { type: 2, path: [0], value: 2 },
  { type: 2, path: [1], value: 3 }
]
*/

4. Circular Reference Safety

Safe comparison of recursive objects without infinite loops.

const a = { id: 1 };
a.self = a;
const b = { id: 2 };
b.self = b;

diff(a, b); 
// Output: [{ type: 2, path: ["id"], value: 2 }]

5. Custom Types via diffWith()

Extend the diffing logic for specialized types like MongoDB ObjectId.

import { diffWith } from "@opentf/obj-diff";
import { ObjectId } from "bson";

const result = diffWith(record1, record2, (a, b) => {
  if (a instanceof ObjectId && b instanceof ObjectId) {
    return a.toString() !== b.toString();
  }
});

---

⚠️ Caveats

Internal Object Sharing (Aliasing)

For maximum performance, @opentf/obj-diff preserves internal object identity (sharing) during the patch() operation.

If your original object contains multiple paths pointing to the same object instance, patching one of those paths will affect all its aliases.

const shared = { x: 1 };
const a = { first: shared, second: shared };
const b = { first: { x: 1 }, second: { x: 2 } };

const d = diff(a, b);
const res = patch(a, d);

// res.first.x will be 2 because it shares the same instance as res.second
console.log(res.first.x); // 2

Tip

If you require independent branches after patching, ensure your input objects do not share internal references that are expected to diverge.

---

📊 Comprehensive Benchmarks

We have rebuilt our benchmark suite using mitata and split it into distinct categories to provide a clear, fair, and comprehensive comparison against the libraries developers actually use.

1. Diff Generation (Speed)

Testing how quickly libraries can detect differences between two structures.

Scenario	@opentf/obj-diff	microdiff	deep-diff	just-diff	deep-object-diff
No changes	1.89 µs	1.85 µs	1.66 µs	2.83 µs	4.37 µs
One property	1.93 µs	1.46 µs	1.24 µs	2.48 µs	3.86 µs
Deep nested (9 lvls)	1.81 µs	1.93 µs	3.18 µs	4.51 µs	3.47 µs
Mixed types (JS native)	1.81 µs	2.21 µs	2.30 µs	2.96 µs	3.70 µs

2. Diff + Patch (Complete Solution)

Testing the full lifecycle: Generating a diff and applying it to reconstruct the target.

Scenario	@opentf/obj-diff	fast-json-patch	jsondiffpatch	rfc6902	just-diff + apply
One property	4.03 µs	2.16 µs	3.82 µs	3.78 µs	4.21 µs
Mixed changes	2.90 µs	2.24 µs	8.46 µs	9.49 µs	4.33 µs

(Note: fast-json-patch is highly optimized for strict JSON, but fails on JS-native structures like Maps/Sets/Dates. Among full-featured libraries, @opentf/obj-diff is significantly faster at patching).

3. Large Scale Payloads (Algorithmic Scalability)

Testing performance on a generated 1 Megabyte JSON payload with one deep change and one insertion.

Metric (1MB JSON)	@opentf/obj-diff	microdiff	jsondiffpatch
Execution Time	33.08 ms	27.36 ms	768.29 ms (Slow)
Diff Size (Bytes)	130 B	198 B	131 B
Memory Allocation	~0 MB	6.45 MB	~0 MB

4. JS-Native Features & Accuracy

Testing modern JavaScript support and complex edge case handling.

Feature	@opentf/obj-diff	microdiff	jsondiffpatch	fast-json-patch
Date	✅	✅	✅	JSON only
Map	✅	❌	❌	❌
Set	✅	❌	❌	❌
TypedArray	✅	✅	✅	❌
Circular Refs	✅	✅	✅	❌
RegExp	✅	✅	✅	❌
Sparse Arrays	✅	✅	✅	JSON only

Conclusion: @opentf/obj-diff offers the exactness and JS-native feature set that JSON-patch libraries lack, while remaining orders of magnitude more scalable than older, heavy libraries like jsondiffpatch.

5. Type-Safe Serialization (stringify/parse vs superjson)

Round-tripping real JavaScript values through a JSON boundary — the job superjson does.

Axis	@opentf/obj-diff	superjson
Type fidelity (22 native types)	22 / 22	14 / 22
Speed (stringify / round trip)	~3× / ~2× faster	baseline
Wire size	smaller for leaf & native-heavy values	smaller when many special values cluster

superjson silently degrades Float64Array specials (NaN/-0/∞ → 0), turns ArrayBuffer/DataView into plain objects, unwraps boxed primitives, drops an Error's own props, and throws on BigInt64Array. Full breakdown on the comparison page.

Running Benchmarks Locally

bun run benchmarks/category-a-diff.js
bun run benchmarks/category-b-patch.js
bun run benchmarks/category-c-large.js
bun run benchmarks/category-d-accuracy.js
bun benchmarks/serialization.mjs   # obj-diff stringify/parse vs superjson

---

❓ FAQs

1. Why is JSON Patch (RFC 6902) not supported?

The JSON Patch protocol is quite heavy and complex. We've optimized @opentf/obj-diff for performance and simplicity, which covers the vast majority of real-world use cases.

2. What does an empty path path: [] mean?

An empty path denotes the Root of the object. It typically means the entire source was replaced by the target value (e.g., comparing an object to null).

---

📄 License

This project is licensed under the MIT License.

---

⚡ Powered by Open Tech Foundation