json-patch-rfc

Forked from fast-json-patch

Tiny, fast utilities fully compatible with RFC 6902 (JSON Patch).

• compare — compute a patch between before → after
• revertOperations — generate inverse ops for rollback
• applyOperations — apply a patch (immutable by default)
• Works in Node and the browser. TypeScript-ready.
• ESM-only; CJS is not supported.

Why you should use JSON-Patch

JSON-Patch (RFC6902) is a standard format that allows you to update a JSON document by sending the changes rather than the whole document. JSON Patch plays well with the HTTP PATCH verb (method) and REST style programming.

Mark Nottingham has a nice blog about it.

Commands

# install
yarn install

# build
yarn build

# test
yarn test

How to use

compare(from: Doc, dest: Doc): Operation[]

Generates a patch that transforms the document from into the document dest.

import { compare } from "json-patch-rfc";

const from = { theme: "light", tags: ["dev"] };
const dest = { theme: "dark", tags: ["dev", "ai"] };

const ops = compare(from, dest);
/*
[
  { op: "replace", path: "/theme", value: "dark" },
  { op: "add", path: "/tags/1", value: "ai" }
]
*/

revertOperations<T extends Doc>(doc: T, ops: Operation[]): Operation[][]

Creates inverse operations for each operation in a patch. Useful to roll back changes step-by-step.

import { revertOperations, applyOperations } from "json-patch-rfc";

const doc = { counter: 0 };
const ops = [
  { op: "replace", path: "/counter", value: 1 }
];

const reverted = revertOperations(doc, ops);
/*
[ [{ op: "replace", path: "/counter", value: 0 }] ]
*/

const updated = applyOperations(doc, ops);
const rolledBack = applyOperations(updated, reverted.flat());
// rolledBack = { counter: 0 }

applyOperations<T>(doc: Doc, operations: ReadonlyArray<Operation>, opts?: { mutate?: boolean }): T

Applies a sequence of operations to a document.

• By default: the doc will not be mutated. It will return a new doc.
• With { mutate: true }: it modifies the doc.

import { applyOperations } from "json-patch-rfc";

const original = { name: "Ada" };
const ops = [{ op: "replace", path: "/name", value: "Ada Lovelace" }];

const updated = applyOperations(original, ops);
// updated = { name: "Ada Lovelace" }
// original remains unchanged