Very fast zlib-compatible compression for JavaScript.

Why pako is cool

Binary-equivalent output. Pako can produce the same deflate/gzip bytes as original zlib (1.3.2) and Node.js' patched zlib.
Tiny browser bundles. Full minified bundle is under 15K gzipped. Deflate-only and inflate-only builds are smaller.
Very fast. Performance is comparable with native zlib in modern JavaScript engines (see benchmarks).

Benchmarks

node v24, 1 MB input sample:

deflate-pako x 14.27 ops/sec ±3.41% (37 runs sampled)
deflate-pako-zlib-hash x 10.60 ops/sec ±0.50% (29 runs sampled)
deflate-zlib x 30.30 ops/sec ±0.61% (51 runs sampled)
gzip-pako x 13.48 ops/sec ±0.50% (36 runs sampled)
inflate-pako x 138 ops/sec ±1.26% (75 runs sampled)
inflate-zlib x 397 ops/sec ±1.37% (81 runs sampled)
ungzip-pako x 125 ops/sec ±1.46% (73 runs sampled)

Install

npm install pako

Examples / API

Full docs - http://nodeca.github.io/pako/

import { Deflate, Inflate, deflate, inflate } from 'pako';
// Deflate
//
const input = new Uint8Array();
//... fill input data here
const output = deflate(input);
// Inflate (simple wrapper can throw exception on broken stream)
//
const compressed = new Uint8Array();
//... fill data to uncompress here
try {
  const result = inflate(compressed);
  // ... continue processing
} catch (err) {
  console.log(err);
}
//
// Alternate interface for chunking & without exceptions
//
const deflator = new Deflate();
deflator.push(chunk1, false);
deflator.push(chunk2); // second param is false by default.
...
deflator.push(chunk_last, true); // `true` says this chunk is last
if (deflator.err) {
  console.log(deflator.msg);
}
const output = deflator.result;
const inflator = new Inflate();
inflator.push(chunk1);
inflator.push(chunk2);
...
inflator.push(chunk_last); // no second param because end is auto-detected
if (inflator.err) {
  console.log(inflator.msg);
}
const output = inflator.result;

For CommonJS:

const { deflate, inflate } = require('pako');

If you need the whole API as an object, use namespace import:

import * as pako from 'pako';

Sometimes you may wish to work with strings — for example, to send stringified objects to a server. Pako's deflate detects the input data type and automatically recodes strings to utf-8 prior to compression. High-level inflate helpers can decode utf-8 output back to JavaScript strings with toText: true.

import { deflate, inflate } from 'pako';
const test = { my: 'super', puper: [456, 567], awesome: 'pako' };
const compressed = deflate(JSON.stringify(test));
const restored = JSON.parse(inflate(compressed, { toText: true }));

Notes

Pako does not contain some specific zlib functions:

deflate - methods deflateCopy, deflateBound, deflateParams, deflatePending, deflatePrime, deflateTune.
inflate - methods inflateCopy, inflateMark, inflatePrime, inflateGetDictionary, inflateSync, inflateSyncPoint, inflateUndermine.
High level inflate/deflate wrappers (classes) may not support some flush modes.

Authors

Andrey Tupitsin @anrd83
Vitaly Puzrin @puzrin

Personal thanks to:

Vyacheslav Egorov (@mraleph) for his awesome tutorials about optimising JS code for v8, IRHydra tool and his advices.
David Duponchel (@dduponchel) for help with testing.

Original implementation (in C):

zlib by Jean-loup Gailly and Mark Adler.

License

MIT - all files, except /src/zlib folder
ZLIB - /src/zlib content