zip.js

zip.js is a JavaScript library (BSD-3-Clause license) for compressing and decompressing zip files. It is designed for high performance and large datasets, supporting:

• Multi-core compression
• Native compression using compression streams
• Archives larger than 4GB via Zip64
• Split zip files
• Data encryption
• Incremental writing
• Deflate64 decompression

For bulk data, zip.js acts as a thin wrapper around the platform's CompressionStream. Consequently, zip.js throughput is primarily determined by the zlib implementation provided by your runtime:

• Deno & Bun: Use zlib-ng, offering the highest throughput (e.g., ~4.8–5.1s for a 256 MB file).
• Node.js: Uses a Chromium zlib fork (e.g., ~8.9s for a 256 MB file).
• WASM Backend: If you disable CompressionStream (using useCompressionStream: false), zip.js uses a classic zlib compiled to WebAssembly. This is the 'portability floor' and is slower than native runtimes (e.g., ~16s for a 256 MB file) but remains competitive with native tools like 7-Zip.

Key Takeaway: The same zip.js code typically runs ~1.75× faster on Deno/Bun than on Node due to the underlying zlib performance.

When choosing a ZIP library, consider these trade-offs based on your use case:

• Use zip.js if you need the fastest compression for large or multiple entries (using parallelism without Web Workers), the fastest large-stream decompression, low-memory streaming of huge files, or advanced ZIP features like AES/ZipCrypto encryption, Zip64, and split/multi-volume archives.
• Use fflate if you need to deflate thousands of tiny buffers in a single call and require the smallest memory footprint and highest raw synchronous throughput.
• Use archiver if you need a solid streaming compressor on Node.js (note: it cannot read archives).
• Use jszip for convenience, but be aware it is slower and buffers whole files in memory.

To ensure you are using the fastest possible configuration in @zip.js/zip.js:

1. Use the default compression level: Requesting a custom level forces a fallback to the WASM zlib codec, which prevents the native CompressionStream from parallelizing via concurrent add() calls.
2. Use concurrent add() calls: Instead of adding entries sequentially, call add() multiple times concurrently to leverage the platform's threadpool.
3. Configure Web Workers for specific runtimes: If running in Deno or Safari/WebKit, ensure you pass useWebWorkers: true to enable true parallelism.

To avoid Content Security Policy (CSP) issues, you can import the WASM module and the worker script as URLs (using tools like Vite's ?url suffix) and provide them to the configure() function via wasmURI and workerURI.

import wasmURI from "@zip.js/zip.js/dist/zip-module.wasm?url";
import workerURI from "@zip.js/zip.js/dist/zip-web-worker.js?url";

configure({
  wasmURI,
  workerURI
});

Handle large files and specific formats:

• zip64: Set to true to use Zip64. Automatically set to true if compressed data exceeds 4GB or has an unknown size. Defaults to false.
• supportZip64SplitFile: Set to false to never write disk numbers in zip64 data. Defaults to true.
• usdz: Set to true to produce zip files compatible with the USDZ specification. Defaults to false.

You can encrypt zip entries using the following options:

• password: A string used to encrypt the content.
• rawPassword: A Uint8Array (or ArrayBufferLike) used for raw password encryption.
• encrypted: Set to true to write encrypted data when passThrough is also true.
• encryptionStrength: The AES encryption strength. Options are 1 (128-bit), 2 (192-bit), or 3 (256-bit). Defaults to 3.
• zipCrypto: A boolean to use the ZipCrypto algorithm. Note: This is not recommended as it is easily broken. Setting this to true automatically sets dataDescriptor to true.

Manage file metadata and encoding:

• creationDate, lastAccessDate, lastModDate: Date objects for file timestamps. These are ignored if extendedTimestamp is false.
• extendedTimestamp: Set to true to store extended timestamp extra fields. If false, dates are limited to a max accuracy of 2 seconds and a max date of November 31, 2107.
• useUnicodeFileNames: Set to true to mark filenames as UTF-8 (setting general purpose bit 11). Defaults to true.