@zokugun/unidiff-strict

Parse and apply unified diffs. Applies patches deterministically, reports rejected hunks, and provides TypeScript types for safety.

Features

• Strict parsing of unified diff format. (No git/svn file operations, No multi-files)
• Deterministic application with clear rejection output.
• TypeScript types with ESM and CJS builds.
• Small footprint.

Installation

npm add @zokugun/unidiff-strict

Quick Start

import { applyUnidiff } from '@zokugun/unidiff-strict';

const source = 'line1\nline2\n';
const diff = `--- a/file\n+++ b/file\n@@ -1,2 +1,3 @@\n line1\n+added\n line2\n`;

// Apply directly from a diff string
const result = applyUnidiff(source, diff, { reject: true });
if(result.fails) {
    throw new Error(res.error);
}

console.log('patched:', res.value.output);
console.log('rejects:', res.value.reject);

API reference

• applyUnidiff(source: string, diff: string | Unidiff, options: ApplyUnidiffOptions): Result<string | { output: string; reject: string }, string>: Apply a diff (string or Unidiff) to source. Returns either the patched string or an object { output, reject } when options.reject is true.
• mergeUnidiff(diffs: Array<Unidiff | string>): DResult<Unidiff>: Merge several unified-diffs into a single Unidiff structure.
• parseUnidiff(source: string): Result<Unidiff, string>: Returns a Unidiff structure from a unified-diff string.
• stringifyUnidiff(diff: Unidiff): string: Returns a unified-diff string from a Unidiff structure.

type ApplyUnidiffOptions = {
	ignorePreviouslyApplied?: boolean;
	reject?: boolean;
};

type Unidiff = {
	hunks: Hunk[];
	newFile?: File;
	oldFile?: File;
};

type Hunk = {
	changes: Change[];
	newLength: number;
	newStart: number;
	oldLength: number;
	oldStart: number;
};

type Change = {
	kind: LineKind;
	text: string;
};

type LineKind = 'context' | 'deletion' | 'insertion';

type File = {
	name: string;
	timestamp?: string;
};

Contributions

Contributions are most welcome. Please:

• Open issues and feature requests under the repository discussions.
• Follow the CONTRIBUTING.md.

Donations

Support this project by becoming a financial contributor.

	ko-fi.com/daiyam
	liberapay.com/daiyam/donate
	paypal.me/daiyam99

License

Copyright © 2026-present Baptiste Augrain

Licensed under the MIT license.