The core compression code I use on my blog for compressing HTML (and other text assets) to Brotli level 11.

compression.js

import { brotliCompressSync } from 'zlib';

/** Default Brotli compression level (0–11). Level 11 gives best ratio, slowest. */
export const BROTLI_LEVEL = 11;

/**
 * Compress a buffer with Brotli.
 * @param {Buffer | Uint8Array | string} input - Input buffer, TypedArray, or string (UTF-8)
 * @param {number} [level=BROTLI_LEVEL] - Brotli level 0–11
 * @returns {Buffer} Compressed buffer
 */
export function brotliCompress(input, level = BROTLI_LEVEL) {
	const buffer = Buffer.isBuffer(input) ? input : Buffer.from(input);
	return brotliCompressSync(buffer, { level });
}