Why I have the following error require is not defined with express?

My server.js file return the following error: ReferenceError: require is not defined

server.js:

import express from 'express'
import { readdirSync } from 'fs';

const app = express()

// Route middleware
readdirSync('./routes').map((route) => 
    app.use('/api', require(`./routes/${route}`))
)

const port = 8000

app.listen(port, () => console.log(`listening on port ${port}`))

Note that in my package.json I use: "type": "module" just to use import instead of require.