but-unzip

but-unzip

small unzip library. ~704 bytes for Node, and ~951^ bytes for browsers, before gzip.

^92.5%+ of browsers support the decompression API, which in 2025, is probably all your users. If you really care about the last 7.5%, you can dynamically import pako, adding ~20k: see below.

Usage

Install via your favorite package manager and import but-unzip. Has zero dependencies.

$ npm install but-unzip

# for old browsers you need
$ npm install pako

This library returns zip entries synchronously, but only returns an entry's uncompressed bytes after calling .read(), which'll give Uint8Array or Promise<Uint8Array>.

Naïve use

If there's a built-in function to inflate compressed files (like in Node or most browsers), you can use the code like:

import { iter } from 'but-unzip';
import * as fs from 'fs';

const bytes = fs.readFileSync('somezip.zip');

for (const entry of iter(bytes)) {
  console.info(entry.name, entry.comment);
  const bytes = await entry.read();
  // do something with bytes
}

Provide inflate function

If you're worried about maximum compatibility:

import { unzip, inflateRaw as platformInflateRaw } from 'but-unzip';
import { inflateRaw as pakoInflateRaw } from 'pako/lib/inflate.js';

async function decompressUint8Array(zipBytes) {
  const allEntries = unzip(zipBytes, platformInflateRaw || pakoInflateRaw);
  // do something with entries
}

Dynamically import inflate

You could use dynamic import() instead to include pako, but the intersection of users who:

• don't have the compression API
• don't support ESM imports

…are extremely high (e.g., IE11 and weird old browsers).

import { inflateRaw as platformInflateRaw } from 'but-unzip';
const inflateRaw = platformInflateRaw || (await import('pako/lib/inflate.js').inflateRaw);

Limitations

• This library doesn't support ZIP64, but probably should. But your browser (and Node) will probably not be happy to work with 4gb+ files, especially as this is not a streaming library (it just gives everything at once).

• Like literally every zip library that exists, this only supports compression types 0 (store) and 8 (deflate).

Notes

• In my testing with esbuild, Pako's ESM bundling can be a bit broken, so importing "pako/lib/inflate.js" adds ~20k. Importing pako wholesale, even if you only use inflateRaw, adds ~45k.

• If you're handling user data and it could be really big, use a Worker. But also, the compression API is async and doesn't block your main thread. YMMV!