double_luhn_validation.js

export const luhn = (value: string) => {
    let nCheck = 0;
    let nDigit = 0;
    let bEven = true;
    const newValue = value.replace(/D/g, '');

    for (let n = newValue.length - 1; n >= 0; n -= 1) {
        const cDigit = newValue.charAt(n);
        nDigit = parseInt(cDigit, 10);

        if (bEven) {
            nDigit *= 2;
            if (nDigit > 9) {
                nDigit -= 9;
            }
        }

        nCheck += nDigit;
        bEven = !bEven;
    }
    return (1000 - nCheck) % 10;
};

export const verifyBarcode = (barcode: string) => {
    const originalCode = barcode.slice(1, -2);
    const raw = `A${originalCode}${luhn(originalCode)}${luhn(
        (parseInt(originalCode, 10) + 1).toString()
    )}`;
    return raw === barcode;
};