Zlib Module in Node.js

Last Updated : 21 Jul, 2026

The zlib module in Node.js is used to compress and decompress data using algorithms like Gzip and Deflate. It helps reduce data size, improving performance and saving bandwidth.

  • Supports compression and decompression of data streams and buffers.
  • Uses Gzip, Deflate, and Inflate algorithms for efficient data compression.
  • Built on the zlib C library, providing reliable and high-performance compression.

Example: Compress a file (demofile.txt) into a gzip file (mygzipfile.txt.gz).

var fs = require('fs');
var zlib = require('zlib');

var x = fs.createReadStream('demofile.txt');
var y = fs.createWriteStream('mygzipfile.txt.gz');
var gzip = zlib.createGzip();
x.pipe(gzip).pipe(y);

Importing Module

To use the zlib module in your Node.js application, simply import it as below:

const zlib = require('zlib');

Zlib Methods

The zlib module provides several methods for compression and decompression.

  • zlib.gzip():zlib.gzip() method compresses data using the Gzip compression algorithm.
  • zlib.gunzip():zlib.gunzip() method decompresses Gzip-compressed data.
  • zlib.deflate(): zlib.deflate() method compresses data using the Deflate algorithm.
  • zlib.inflate(): zlib.inflate() method decompresses Deflate-compressed data.
  • zlib.deflateRaw(): zlib.deflateRaw() method compresses data using the Deflate algorithm without headers or checksums.
  • zlib.inflateRaw(): zlib.inflateRaw() method decompresses data that was compressed using deflateRaw().
  • zlib.brotliCompress(): zlib.brotliCompress() method compresses data using the Brotli compression algorithm.
  • zlib.brotliDecompress(): zlib.brotliDecompress() method decompresses Brotli-compressed data.

Example 1: Compressing a String

Node 
const zlib = require('zlib');

const s_in = 'This is a sample string to compress.';

zlib.gzip(s_in, (err, compressedBuffer) => {
    if (err) {
        console.error('Compression error:', err);
    } else {
        console.log('Compressed Buffer:', compressedBuffer);
        console.log('Compressed Buffer (Hex):', compressedBuffer.toString('hex'));
    }
});

Output:

Screenshot-2024-08-12-143811
compression

Example 2: Decompressing a Gzip Buffer

Node 
console.clear();
const zlib = require("zlib");

const compressedBuffer = Buffer.from("your_hex_string_here", "hex");
zlib.gunzip(compressedBuffer, (err, buffer) => {
    if (err) {
        console.error("Error decompressing:", err);
    } else {
        console.log("Decompressed String:", buffer.toString());
    }
});

Output:

Screenshot-2024-08-10-233639
Gzip Buffer

Benefits of Zlib Module

The zlib module improves data compression efficiency and performance in Node.js applications.

  • Reduces Storage Space: Compresses data to minimize disk storage requirements.
  • Improves Data Transfer: Decreases data size, resulting in faster network transmission.
  • Enhances Performance: Stream-based compression efficiently processes large files with lower memory usage.
  • Provides Flexible Compression: Supports multiple compression algorithms and configurable compression levels for different requirements.

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