common.ts

export const validFødselsnummer = (id: string): boolean => {
    const weights1 = [3, 7, 6, 1, 8, 9, 4, 5, 2];
    const weights2 = [5, 4, 3, 2, 7, 6, 5, 4, 3, 2];

    const sum = (id: number[], factors: number[]) =>
        factors.map((f, i) => f * id[i]).reduce((acc, curr) => acc + curr, 0);

    const checksum = (id: number[], weigths: number[]) => (11 - (sum(id, weigths) % 11)) % 11;

    if (id?.trim().length != 11) return false;

    const idAsArray: number[] = id.split('').map((c) => parseInt(c, 10));

    if (checksum(idAsArray, weights1) != idAsArray[9]) return false;

    return checksum(idAsArray, weights2) == idAsArray[10];
};