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Tiny Merge Patch

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An implementation of the JSON Merge Patch RFC 7396: a standard format used to describe modifications to JSON documents.

This library complies with the functional programming style: it does not mutate the original target, but recycles what it can. It is particularly appropriate to update a state used by React, allowing selective re-rendering of the UI.

tiny-merge-patch passes all RFC 7396 tests.

Install

Install the current version (and save it as a dependency):

npm

npm install tiny-merge-patch --save

Import

CommonJs with node

// Fetch `apply` from the module.
const mergePatch = require('tiny-merge-patch').apply;

ES modules in the browser

// `apply` is also the default export.
import mergePatch from 'https://unpkg.com/tiny-merge-patch/esm/index.js'

Usage

// Original document / object.
const doc = {
  a: 'b',
  c: { d: 'e', f: 'g' },
  h: { i: 0 }
};

// JSON merge patch to apply.
const patch = {
  a: 'z',
  c: { f: null } // null marks deletions.
};

// Apply the patch.
const patchedDoc = mergePatch(doc, patch);

// tiny-merge-patch complies with the RFC specification.
assert.deepEqual(patchedDoc, {
  a: 'z',
  c: { d: 'e' },
  h: { i: 0 },
});

// Additionally, it does not mutate the original document...
assert(patchedDoc !== doc);

// ...nor its content...
assert(patchedDoc.c !== doc.c);

// ...but recycles what it can.
assert(patchedDoc.h === doc.h);

Alternatives

All are in-place. To avoid mutations of the original object, one can deep-clone beforehand, but it can be expensive. At the contrary, tiny-merge-patch does not alter any of its arguments—but recycles what it can. Recycling also allows efficient strict identity-based memoization (used by React's PureComponent for example).

All of the above libraries also embed additional functionalities, such as patch generation from two objects or merge of patches. tiny-merge-patch only focuses on the IETF standard and on patch applications.

(None of the above libraries are particularly big. Still, tiny-merge-patch is smaller if you only need to apply patches. It is also worth mentioning that unlike JSON patches, there is no way to implement merge of merge patches that reliably preserves deletion.)

License

MIT