Compress data with node:zlib

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The node:zlib module is built into Deno and offers more codecs and options than the web standard streams, including brotli and synchronous one-shot helpers. For simple gzip and deflate streaming, the web standard CompressionStream in /examples/compress_decompress/ needs no imports at all.

import {
  brotliCompressSync,
  brotliDecompressSync,
  gunzipSync,
  gzip,
  gzipSync,
} from "node:zlib";
import { promisify } from "node:util";

We compress some repetitive data, which compresses well.

const input = new TextEncoder().encode("Hello Deno! ".repeat(100));

To compress a buffer in one call, use gzipSync. The result is a Buffer, which is a Uint8Array subclass.

const gzipped = gzipSync(input);
console.log(input.length, "->", gzipped.length); // 1200 -> 47

To decompress, use gunzipSync. The round trip restores the exact bytes.

const restored = gunzipSync(gzipped);
console.log(new TextDecoder().decode(restored).slice(0, 11)); // Hello Deno!
console.log(restored.length === input.length); // true

The sync functions block the event loop while they run. In a server, promisify the callback variant and await it instead.

const gzipAsync = promisify(gzip);
const gzipped2 = await gzipAsync(input);
console.log(gzipped2.length); // 47

node:zlib also implements brotli, which CompressionStream does not offer. Brotli usually compresses text harder than gzip.

const brotli = brotliCompressSync(input);
console.log(brotli.length); // 30
console.log(brotliDecompressSync(brotli).length); // 1200

Run this example locally using the Deno CLI:

deno run https://docs.deno.com/examples/scripts/zlib_compression.ts

Compress data with node:zlib

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