is-bzip2 
Check if a Buffer/Uint8Array is a BZIP2 file
Install
$ npm install --save is-bzip2
Usage
var isBzip2 = require('is-bzip2');
var read = require('fs').readFileSync;
isBzip2(read('foo.bz2'));
// => true
Check if a Buffer/Uint8Array is a BZIP2 file