Two one-liners for browsers, one for packing data into .gz format, the other to unpack. Requires Compression Streams API.

pack-unpack-gzip-file.js

// works for modern browsers supporting Compression Streams API - https://developer.mozilla.org/en-US/docs/Web/API/Compression_Streams_API
const unpackGzip = buffer => new Response(new Blob([buffer]).stream().pipeThrough(new DecompressionStream('gzip'))).arrayBuffer();
const packGzip = buffer => new Response(new Blob([buffer]).stream().pipeThrough(new CompressionStream('gzip'))).arrayBuffer();