Hey @olitares,

This should do the trick: 
 

<script>
// Encapsulating the original CPF validation logic in a function
function validateCPF(cpfValue) {
    var cpf = cpfValue.replace(/(^\d]+/g, '');
    if (cpf == '' || cpf.length != 11) return false;
    if (/^(.)\1+$/.test(cpf)) return false; // Simplified check for repeated numbers

    var add = 0, rev;
    for (var i = 0; i < 9; i++)
        add += parseInt(cpf.charAt(i)) * (10 - i);
    rev = 11 - (add % 11);
    if (rev == 10 || rev == 11) rev = 0;
    if (rev != parseInt(cpf.charAt(9))) return false;

    add = 0;
    for (var i = 0; i < 10; i++)
        add += parseInt(cpf.charAt(i)) * (11 - i);
    rev = 11 - (add % 11);
    if (rev == 10 || rev == 11) rev = 0;
    if (rev != parseInt(cpf.charAt(10))) return false;

    return true; // CPF is valid
}

// Bind the validation to the CPF field
document.addEventListener('DOMContentLoaded', function() {
    var cpfField = document.getElementById('cpf'); // Adjust the selector as needed
    if (cpfField) {
        cpfField.addEventListener('blur', function() {
            var isValidCPF = validateCPF(cpfField.value);
            if (!isValidCPF) {
                alert('CPF INVÁLIDO'); // Provide feedback or handle invalid CPF as needed
                // Consider adding more sophisticated feedback mechanisms, such as displaying an error message next to the input field
            }
        });
    }
});
</script>

 I didn’t have too much time to style it and/or display the error message around the field but it should work. 

 

Hi Hristian, It worked perfectly, I was scratching my head about it... Thank you very much