is-gzip 
Check if a Buffer/Uint8Array is a GZIP file
Install
$ npm install --save is-gzip
Usage
var isGzip = require('is-gzip');
var read = require('fs').readFileSync;
isGzip(read('foo.tar.gz'));
// => true
Check if a Buffer/Uint8Array is a GZIP file
$ npm install --save is-gzip
var isGzip = require('is-gzip');
var read = require('fs').readFileSync;
isGzip(read('foo.tar.gz'));
// => true