jsonc-patch

Apply object changes to a JSON / JSONC string while preserving formatting, comments, and original whitespace style.

jsoncPatch diffs your source text against a target object and replays the changes in place, so comments, trailing commas, indentation, and spacing all survive the edit.

How it works

1. The source text is parsed with jsonc-parser.
2. The diff between the parsed source and the target object is computed with fast-json-patch (RFC 6902).
3. Each patch operation is replayed through jsonc-parser's modify(), so the output keeps all original formatting.

Removals are applied before adds/replaces and paths are sorted in reverse order to avoid index-shifting bugs when patching arrays.

Install

npm install jsonc-patch

pnpm add jsonc-patch

Usage

import { jsoncPatch } from 'jsonc-patch'
// or: import jsoncPatch from 'jsonc-patch'

jsoncPatch('{ "a": 1 }', { a: 1, b: 2 })
// => '{ "a": 1, "b": 2 }'

Add a property

jsoncPatch('{ "a": 1 }', { a: 1, b: 2 })
// => '{ "a": 1, "b": 2 }'

Update a property

jsoncPatch('{ "a": 1, "b": 2 }', { a: 1, b: 3 })
// => '{ "a": 1, "b": 3 }'

Remove a property

jsoncPatch('{ "a": 1, "b": 2 }', { a: 1 })
// => '{ "a": 1 }'

Preserve comments

jsoncPatch('{ /* hello */ "a": 1 }', { a: 2 })
// => '{ /* hello */ "a": 2 }'

Preserve trailing commas

jsoncPatch('{ "a": 1, }', { a: 2 })
// => '{ "a": 2, }'

Array operations (index-aware)

jsoncPatch('{ "arr": [1, 2, 3] }', { arr: [1, 4, 3] })
// => '{ "arr": [1, 4, 3] }'

Nested updates

jsoncPatch('{ "a": { "x": 1 } }', { a: { x: 2 } })
// => '{ "a": { "x": 2 } }'

Empty input defaults to {}

jsoncPatch('', { foo: 'bar' })
// => '{ "foo": "bar" }'

Control spacing via options

jsoncPatch('{"a":1}', { a: 2 }, { formattingOptions: { insertSpaces: true, tabSize: 2 } })
// => '{\n  "a": 2\n}'

API

function jsoncPatch<T extends object>(
  text: string,
  object: T,
  options?: ModificationOptions
): string

• text — Original JSON / JSONC text. If empty or falsy, defaults to "{}".
• object — Target plain object whose properties become the result.
• options — Optional ModificationOptions forwarded to jsonc-parser's modify().

Returns the updated JSONC string.

License

MIT