JavaScript function to validate the Swiss AHV number

ahv_validate.js

// Documentation: https://www.sozialversicherungsnummer.ch/aufbau-neu.htm

function isValidAHVNumber(ahvNumber) {
    // Remove dots from the AHV number
    let cleanedAhvNumber = ahvNumber.replace(/\./g, '');

    if (!/^\d{13}$/.test(cleanedAhvNumber)) {
        return false; // Checks if the AHV number is exactly 13 digits after removing dots
    }

    if (cleanedAhvNumber.substring(0, 3) !== '756') {
        return false; // Checks the country code
    }

    // Calculate the check digit using the EAN13 algorithm
    let sum = 0;
    for (let i = 11; i >= 0; i--) {
        let factor = (11 - i) % 2 === 0 ? 3 : 1;
        sum += parseInt(cleanedAhvNumber[i]) * factor;
    }
    let checkDigit = (10 - (sum % 10)) % 10;

    // Compare calculated check digit with the last digit of cleaned AHV number
    return checkDigit === parseInt(cleanedAhvNumber[12]);
}

// Example usage
document.getElementById('ahv_field').addEventListener('input', function() {
    let errorMessage = document.getElementById('ahv-error-message');
    if (!isValidAHVNumber(this.value)) {
        errorMessage.style.display = 'block';
    } else {
        errorMessage.style.display = 'none';
    }
});