but-unzip

small unzip library. ~666 bytes for Node 😈, and ~755^ bytes for browsers, before gzip.

^95% of browsers support the decompression API, which in 2026, is effectively all your users. For niche use cases, you should import pako.

Usage

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

$ npm install but-unzip

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';

// in node, get bytes like this (or get a Uint8Array some other way)
import * as fs from 'fs';
const bytes = fs.readFileSync('somezip.zip');

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

Just like that!

Provide inflate function

If you're worried about maximum compatibility, add pako as a dependency and include its inflateRaw method:

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
}

Again, this is for a tiny minority of users who can't practically use the modern web anyway.

Notes

• This library doesn't support ZIP64. However, your browser (and Node) will likely 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).

• 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!