# @electron/asar > Creating Electron app packages Latest version **4.3.1** (published 2026-09-26) · MIT license · 0 weekly downloads ## Install ```sh npm install @electron/asar pnpm add @electron/asar yarn add @electron/asar bun add @electron/asar ``` Provides the command `asar`. ## Health **Score 75/100 (B)** — status: active. Positive: has types; esm support; no vulnerabilities; has provenance; recently updated; high maintenance score; high quality score. Warnings: low downloads. ## Facts | | | |---|---| | Version | 4.3.1 | | Published | 2026-09-26 | | First published | 2022-10-18 | | Weekly downloads | 0 | | License | MIT | | TypeScript types | bundled | | Module format | ESM | | Node | >=22.12.0 | | Dependencies | 2 | | Unpacked size | 123 KB | | Known vulnerabilities | 0 | | Install scripts | no | | Provenance | attested (GitHub Actions) | | GitHub stars | 2866 | | Maintainers | electron-cfa | ## Links - npm: https://www.npmjs.com/package/@electron/asar - Repository: https://github.com/electron/asar - Issues: https://github.com/electron/asar/issues - npm.io page: https://npm.io/package/@electron/asar ## Dependencies (2) - [glob](https://npm.io/package/glob.md) ^13.0.2 - [minimatch](https://npm.io/package/minimatch.md) ^10.0.1 ## Recent versions - 4.3.1 (latest) — 2026-09-26 - 4.3.0 — 2026-08-18 - 4.2.1 — 2026-07-21 - 4.2.0 — 2026-03-31 - 4.1.2 — 2026-03-28 - 4.1.1 — 2026-03-24 - 4.1.0 — 2026-03-05 - 4.0.1 — 2025-08-02 - 4.0.0 — 2025-05-14 - 3.4.1 — 2025-04-07 - 3.4.0 — 2025-04-02 - 3.3.1 — 2025-02-11 - 3.3.0 — 2025-02-10 - 3.2.18 — 2025-01-07 - 3.2.17 — 2024-11-07 - … 17 more at https://npm.io/package/@electron/asar/versions ## README # @electron/asar - Electron Archive [![Test](https://github.com/electron/asar/actions/workflows/test.yml/badge.svg)](https://github.com/electron/asar/actions/workflows/test.yml) [![npm version](http://img.shields.io/npm/v/@electron/asar.svg)](https://npmjs.org/package/@electron/asar) [![API docs](https://img.shields.io/badge/dynamic/json?url=https%3A%2F%2Fregistry.npmjs.org%2F%40electron%2Fasar%2Flatest&query=%24.version&logo=typescript&logoColor=white&label=API%20Docs)](https://packages.electronjs.org/asar) ASAR is a simple extensive archive format. It concatenates all files together without compression (like [`tar`](https://www.gnu.org/software/tar/)) while having random access support. ## Features * Support random access * Use JSON to store file information * Very easy to write a parser * Store the contents of duplicated files only once ## CLI ### Install This module requires Node 22.12.0 or later. ```bash npm install --engine-strict @electron/asar ``` ### Usage ```bash $ asar --help Usage: asar [options] [command] Commands: pack|p create asar archive list|l list files of asar archive extract-file|ef extract one file from archive extract|e extract archive Options: -h, --help output usage information -V, --version output the version number ``` #### Excluding multiple resources from being packed Given: ```text app (a) ├── x1 (b) ├── x2 (c) ├── y3 (d) │   ├── x1 (e) │   └── z1 (f) │   └── x2 (g) └── z4 (h) └── w1 ``` Exclude: a, b ```bash asar pack app app.asar --unpack-dir "{x1,x2}" ``` Exclude: a, b, d, f ```bash asar pack app app.asar --unpack-dir "**/{x1,x2}" ``` Exclude: a, b, d, f, h ```bash asar pack app app.asar --unpack-dir "{**/x1,**/x2,z4/w1}" ``` ## Programmatic usage For full API usage, see the [API documentation](https://packages.electronjs.org/asar). ### Example ```javascript import { createPackage } from '@electron/asar'; const src = 'some/path/'; const dest = 'name.asar'; await createPackage(src, dest); console.log('done.'); ``` Please note that there is currently **no** error handling provided! ### Deduplication Files with identical contents are stored once and shared: the first copy is written into the archive and every other copy's header entry points at that same `offset`. Nothing changes for readers — each file still has its own entry, size, integrity hash, and executable bit — but archives with duplicated contents (a common shape for bundled `node_modules`) get smaller and pack faster, since the redundant bytes are never written. Unpacked files (`unpack` / `unpackDir`) are always written out in full, because they live on disk outside the archive. ### Transform You can pass in a `transform` option, that is a function, which either returns nothing, or a `stream.Transform`. The latter will be used on files that will be in the `.asar` file to transform them (e.g. compress). ```javascript import { createPackageWithOptions } from '@electron/asar'; const src = 'some/path/'; const dest = 'name.asar'; function transform (filename) { return new CustomTransformStream() } await createPackageWithOptions(src, dest, { transform: transform }); console.log('done.'); ``` ## Format Asar uses [Pickle][pickle] to safely serialize binary value to file. The format of asar is very flat: ```markdown | UInt32: header_size | String: header | Bytes: file1 | ... | Bytes: file42 | ``` The `header_size` and `header` are serialized with [Pickle][pickle] class, and `header_size`'s [Pickle][pickle] object is 8 bytes. The `header` is a JSON string, and the `header_size` is the size of `header`'s `Pickle` object. Structure of `header` is something like this: ```json { "files": { "tmp": { "files": {} }, "usr" : { "files": { "bin": { "files": { "ls": { "offset": "0", "size": 100, "executable": true, "integrity": { "algorithm": "SHA256", "hash": "...", "blockSize": 1024, "blocks": ["...", "..."] } }, "cd": { "offset": "100", "size": 100, "executable": true, "integrity": { "algorithm": "SHA256", "hash": "...", "blockSize": 1024, "blocks": ["...", "..."] } } } } } }, "etc": { "files": { "hosts": { "offset": "200", "size": 32, "integrity": { "algorithm": "SHA256", "hash": "...", "blockSize": 1024, "blocks": ["...", "..."] } } } } } } ``` `offset` and `size` records the information to read the file from archive, the `offset` starts from 0 so you have to manually add the size of `header_size` and `header` to the `offset` to get the real offset of the file. Files with identical contents share a single copy in the archive, so more than one entry can point at the same `offset`. `offset` is a UINT64 number represented in string, because there is no way to precisely represent UINT64 in JavaScript `Number`. `size` is a JavaScript `Number` that is no larger than `Number.MAX_SAFE_INTEGER`, which has a value of `9007199254740991` and is about 8PB in size. We didn't store `size` in UINT64 because file size in Node.js is represented as `Number` and it is not safe to convert `Number` to UINT64. `integrity` is an object consisting of a few keys: * A hashing `algorithm`, currently only `SHA256` is supported. * A hex encoded `hash` value representing the hash of the entire file. * An array of hex encoded hashes for the `blocks` of the file (i.e. for a blockSize of 4KB, this array contains the hash of every block if you split the file into N 4KB blocks). * A integer value `blockSize` representing the size in bytes of each block in the `blocks` hashes above. [pickle]: https://chromium.googlesource.com/chromium/src/+/main/base/pickle.h --- _Source: https://npm.io/package/@electron/asar · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._