rövardansen.js

function encrypt (str) {
    return str.replace(/([^aeiouöäå01-9])/gi, (c) => { return `${c}o${c}`; });
}

function decrypt (str) {
    return str.replace(/([^aeiouöäå01-9])o([^aeiouöäå01-9])/gi, (origin, first, last) => {
        return (first == last)? first: origin; 
    });
}

let encrypted = encrypt("Rövarspråket");  // "RoRövovarorsospoproråkoketot"
let decrypted = decrypt(encrypted);  // "Rövarspråket"