Express minimal

const express = require('express')
const app = express()
const port = 3000

let urlap=`
<form>
    <input type="number" placeholder="egyik szám" name=x1><br>
    <input type="number" placeholder="másik szám" name=x2><br>
    <button>Szoroz</button>
</form>`;

f= (x,y) => `
A két beírt szám szorzata: ${ x } * ${ y } = ${ x * y }
<br>
<a href="/">Vissza az űrlaphoz</a>
`

app.get('/', (req, res) => {
    let adat = new Map
    let input = req.url.split("?")
    if (input.length > 1) {
        input[1].split("&").forEach(v => {
            let q=v.split("=")
            adat.set(q[0], q[1])
        })
    }
    res.send( !adat.size ? urlap : f( adat.get('x1'), adat.get('x2') ) )
})

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