after changing the req.url we have to set the Content-Type Header manually, otherwise it is set to application/octet-stream

express-brotli-content-type-thing

const express = require('express')
const mime = require('mime')
const fs = require('fs')

const server = express()

server.get(/\.(js|css)$/, (req, res, next) => {
  if (req.header('Accept-Encoding').includes('br')) {
    if (fs.existsSync(`${config.path}${req.url}.br`)) {
      const type = mime.lookup(req.path)
      const charset = mime.charsets.lookup(type)
      req.url += '.br'

      res.set('Content-Encoding', 'br')
      res.set("Content-Type", type + (charset ? "; charset=" + charset : ""))
    }
  }
  next()
})