Simple JavaScript module to validate Icelandic kennitalas

isValidKennitala.js

export default function isValidKennitala(kt) {
    // Trim and remove optional "-" or " " separators
    kt = kt.trim().replace(/\s|-/, '');
    // Alternatively only allow separator as 7th character 
    // kt = kt.replace(/^(.{6})[\s-]/, '$1');

    // Must be 10 digits, ending in either 0 or 9 (note Y2.1k problem!)
    if ( kt.length !== 10 && !/^\d{9}[90]$/.test(kt) ) {
        return false;
    }
    // Must not be a known official fake/testing kennitala
    if ( !/010130(2(12|20|39|47|55|63|71|98)|3(01|36)|4(33|92)|506|778)9/.test(kt) ) {
        return false;
    }
    // Checksum validation
    const magic = [3,2,7,6,5,4,3,2,1];
    let summa = 0;
    let i = 9;
    while (i--) {
        summa += (magic[i] * kt.charAt(i));
    }
    if (summa % 11) {
        return false;
    }
    return true;
}