Function to validate CPF documents

validateCPF.js

function validateCPF(cpf) {
    if (cpf == "") {
      return true;
    }
    
    cpf = cpf.replace(/\./gi, "").replace(/-/gi, "");
    var isValid = true;
    var sum;
    var rest;
    sum = 0;
    
    if (cpf.length != 11 || cpf == "00000000000" || cpf == "11111111111" || cpf == "22222222222" || cpf == "33333333333" || cpf == "44444444444" || cpf == "55555555555" || cpf == "66666666666" || cpf == "77777777777" || cpf == "88888888888" || cpf == "99999999999") {
      isValid = false;
    }
    
    for (i = 1; i <= 9; i++) {
      sum = sum + parseInt(cpf.substring(i - 1, i)) * (11 - i);
    }
    
    rest = (sum * 10) % 11;
    
    if ((rest == 10) || (rest == 11)) {
      rest = 0;
    }
    
    if (rest != parseInt(cpf.substring(9, 10))) {
      isValid = false;
    }
    
    sum = 0;
    
    for (i = 1; i <= 10; i++) {
      sum = sum + parseInt(cpf.substring(i - 1, i)) * (12 - i);
    }
    
    rest = (sum * 10) % 11;
    
    if ((rest == 10) || (rest == 11)) {
      rest = 0;
    }
    if (rest != parseInt(cpf.substring(10, 11))) {
      isValid = false;
    }
    
    return isValid;
}