chirp: 'Twitter' Networks Analyser

is-jpg

Check if a Buffer/Uint8Array is a JPEG image

$ npm install is-jpg

Node.js

const readChunk = require('read-chunk');
const isJpg = require('is-jpg');
const buffer = readChunk.sync('unicorn.jpg', 0, 3);

isJpg(buffer);
//=> true

Browser

const xhr = new XMLHttpRequest();
xhr.open('GET', 'unicorn.jpg');
xhr.responseType = 'arraybuffer';

xhr.onload = () => {
    isJpg(new Uint8Array(this.response));
    //=> true
};

xhr.send();

Accepts a Buffer (Node.js) or Uint8Array.

It only needs the first 3 bytes.