Function to validate brazilian CPF

validate-cpf.js

/* 
 *  Validates a CPF number
 *  @param   String:  cpfString     // User CPF (just numbers or formated(000.000.000-00))
 *  @return  Boolean: success/false // Returns if is valid
 *  Reference and logic: https://www.devmedia.com.br/validar-cpf-com-javascript/23916
 *  Official code: http://www.receita.fazenda.gov.br/aplicacoes/atcta/cpf/funcoes.js
 */
function validateCpf(cpfString: string): boolean {
  let validated = false; // Start with false

  // Checking cpf lenght
  if (cpfString.length !== 14 && cpfString.length !== 11) {
    return validated;
  }

  // Checking for "formated cpf (000.000.000-00)" and replace "points"
  if (cpfString.length === 14) {
    cpfString = cpfString.replace('.', '');
    cpfString = cpfString.replace('.', '');
    cpfString = cpfString.replace('-', '');
  }

  // Variables to check cpf valid (sum and rest)
  let sum = 0, rest = 0;

  // Checking for "null" CPF
  if (cpfString === '00000000000') {
    return validated;
  }

  // sum numbers
  for (let i = 1; i <= 9; ++i) {
    sum += (parseInt(cpfString.substring(i - 1, i)) * (11 - i));
  }

  // Getting rest
  rest = (sum * 10) % 11;

  if ((rest == 10) || (rest == 11)) {
    rest = 0;
  }

  if (rest != parseInt(cpfString.substring(9, 10))) {
    return validated;
  }

  validated = true;
  return validated;
}