How to determine the file type on the server when transferring it with socket.io?

Question

JavaScript

I transfer the file to the server using socket.io.
Determining the format on the client side is not a problem, however, a bunch of bits come to the server, and it is not clear how to determine which format with their help.
Send like thissocket.emit('send-file', file.name, buffer);

Answer 1

Option two:

Determine the mime type on the server side directly from the data by the "magic" header, https://github.com/mscdex/mmmagic