Roman Number To Decimal v2

<!DOCTYPE html>
<html lang="hu">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Római szémok</title>
</head>
<body>

<form action="post">
<label for="inputR">Római szám:</label>
<input type="text" name="inputRomai" id="inputR">

<button type="submit" onclick="RomanToInt(document.getElementById('inputR').value)">Átvált</button>

</form>


<script>
"use strict"

function RomanToInt(s)
{


const RomanN = {
    "I":1,
    "V":5,
    "X":10,
    "L":50,
    "C":100,
    "D":500,
    "M":1000
}
let sum =0
let num =0
let pattern = "[IVXLCDM]"

const re = new RegExp(pattern)

if (re.exec(s,pattern))
{


    for (let i = 0; i < s.length; i++)
    {
        let currentChar = s[i]


        num = RomanN[currentChar]


        if ((i + 1 < s.length) && (RomanN[s[i+1]] > RomanN[currentChar]))
        {
            sum -= num
        }
        else
        {
            sum += num
        }
    }
}
else{
document.write("Római számot nem tartalmaz")

}
    document.write(sum)

}
//RomanToInt("VIII");


</script>


</body>
</html>