JSON Patch for API Client

This library is based on JSON8 library by Sonny Piers.

Introduction

JSON Patch RFC 6902 (and diff) implementation for JavaScript as ESM.

See jsonpatch.com for more information about JSON Patch.

Getting started

npm install @api-client/json

import { Patch } from '@api-client/json';

For performance concerns the Patch may mutate target document; if you want it to use its own copy use:

import { Patch, Core } from '@api-client/json';

const myDocument = { foo: "bar" };
const doc = Core.clone(myDocument);

The Patch never mutates patches.

Methods

apply

import { Patch } from '@api-client/json';

doc = Patch.apply(doc, patch).doc;

Patch.apply (and other Patch methods) returns an object with a doc property because per specification a patch can replace the original root document.

The operation is atomic, if any of the patch operation fails, the document will be restored to its original state and an error will be thrown.

patch

Alias for apply() method.

revert

If the patch() or apply() method is called with a third argument {reversible: true} it will return an additional value in the form of a revert property.

The revert object can be used to revert a patch on a document.

import { Patch } from '@api-client/json';

// apply the patch with the reversible option
const applyResult = Patch.apply(doc, patch, { reversible: true });
doc = applyResult.doc;

// revert the patch
doc = Patch.revert(doc, applyResult.revert).doc;
// doc is strictly identical to the original

See also buildRevertPatch() which offers more flexibility.

buildRevertPatch

Builds a valid JSON Patch from the result of a reversible apply operation. You can then use this patch with apply() method to revert a previously applied patch.

import { Patch } from '@api-client/json';

// apply the patch
const applyResult = Patch.apply(doc, patch, { reversible: true });
doc = applyResult.doc;

// revert the patch
const revertPatch = Patch.buildRevertPatch(applyResult.revert); // this is a valid JSON Patch
doc = Patch.apply(doc, revertPatch).doc;
// doc is strictly identical to the original

Because buildRevertPatch() + apply() offers more flexibility over revert() it is preferred.

• use pack()/unpack() with the result of buildRevertPatch() making it ideal for storage or transport
• reverse a revert (and so on...) with {reversible: true}
• diff() between reverts
• merge multiple reverts into one
• rebase reverts

diff

Returns a diff in the form of a JSON Patch for 2 JSON values.

import { Patch } from '@api-client/json';

Patch.diff(true, false);
// [{"op": "replace", "path": "", "value": "false"}]

Patch.diff([], []);
// []

Patch.diff({}, { foo: "bar" });
// [{"op": "add", "path": "/foo", "value": "bar"}]

valid4

Returns true if the patch is valid, false otherwise.

This method only check for JSON Patch semantic. If you need to verify the patch is JSON valid, use valid().

import { Patch } from '@api-client/json';

Patch.valid({})  // false
Patch.valid([{}] // false
Patch.valid([{op: "foo", path: null, value: undefined}]) // false
Patch.valid([{op: "add", path: "/foo"}]) // false

Patch.valid([]) // true
Patch.valid([{op: "add", path: "/foo", value: "bar"}]) // true

Operations

add, copy, replace, move, remove, test operations return an object of the form {doc: document, previous: value}

• doc is the patched document
• previous is the previous/replaced value

add

doc = Patch.add(doc, "/foo", "foo").doc;

remove

doc = Patch.remove(doc, "/foo").doc;

replace

doc = Patch.replace(doc, "/foo", "foo").doc;

move

doc = Patch.move(doc, "/foo", "/bar").doc;

copy

doc = Patch.copy(doc, "/foo", "/bar").doc;

test

doc = Patch.test(doc, "/foo", "bar").doc;

Extra operations

Those are not part of the standard and are only provided for convenience.

get

Patch.get(doc, "/foo");
// returns value at /foo

has

Patch.has(doc, "/foo");
// returns true if there is a value at /foo

Patch size

Per specification patches are pretty verbose. The library provides pack() and unpack() methods to reduce the size of patches and save memory/space/bandwidth.

Size (in bytes) comparison for the following patch file

[
  { "op": "add", "path": "/a/b/c", "value": ["foo", "bar"] },
  { "op": "remove", "path": "/a/b/c" },
  { "op": "replace", "path": "/a/b/c", "value": 42 },
  { "op": "move", "from": "/a/b/c", "path": "/a/b/d" },
  { "op": "copy", "from": "/a/b/c", "path": "/a/b/e" },
  { "op": "test", "path": "/a/b/c", "value": "foo" }
]

| format | size (in bytes) | | :-----------: | :-------------: | | unpacked | 313 | | unpacked gzip | 148 | | packed | 151 | | packed gzip | 99 |

In practice I'd recommand to use pack/unpack if

• data compression cannot be used on the transport of the patch
• keeping a large amount of patches in memory/on disk

pack

const patch = [
  { op: "add", path: "/a/b/c", value: ["foo", "bar"] },
  { op: "remove", path: "/a/b/c" },
  { op: "replace", path: "/a/b/c", value: 42 },
  { op: "move", from: "/a/b/c", path: "/a/b/d" },
  { op: "copy", from: "/a/b/c", path: "/a/b/e" },
  { op: "test", path: "/a/b/c", value: "foo" },
];

const packed = Patch.pack(patch);

Here is what packed looks like

[
  [0, "/a/b/c", ["foo", "bar"]],
  [1, "/a/b/c"],
  [2, "/a/b/c", 42],
  [3, "/a/b/d", "/a/b/c"],
  [4, "/a/b/e", "/a/b/c"],
  [5, "/a/b/c", "foo"]
]

unpack

const patch = Patch.unpack(packed);
// [{...}, {...}, ...]