archive-type 
Detect the archive type of a Buffer/Uint8Array
See archive-type-cli for the command-line version.
Install
$ npm install --save archive-type
Usage
var readFileSync = require('fs').readFileSync;
var archiveType = require('archive-type');
archiveType(readFileSync('foo.zip'));
//=> {ext: 'zip', mime: 'application/zip'}
API
archiveType(buf)
Returns 7z, bz2, gz, rar, tar, zip, xz or false.
buf
Type: buffer (Node.js), uint8array
It only needs the first 261 bytes.
License
MIT © Kevin Mårtensson