CPF and CNPJ validators

cpfcnpj.js

String.prototype.pad = function (length) {
  'use strict';
  var s = this;
  while (s.length < length) {
    s = '0' + s;
  }
  return s;
};
String.prototype.numbers = function () {
  'use strict';
  var result = '';
  if (this.match(/(\d+)/g)) {
    result = this.match(/(\d+)/g).join('');
  }
  return result;
};
String.prototype.isCPF = function () {
  'use strict';
  // Keep only numbers, inserts leading zeros ensuring correct size.
  var cpf = this.numbers().pad(11),
    valid = true,
    sum,
    n,
    i,
    d;
  // Ignore false positives when only repeating single number.
  if (/^(\d)\1+$/.test(cpf)) {
    return false;
  }
  // Interaction for each check digit.
  for (n = 0; n < 2; n += 1) {
    sum = 0;
    // Multiply positions by decreasing 10 and 11 in the second interaction, accumulating the sum.
    for (i = 10 + n; i > 1; i -= 1) {
      sum += cpf.substr(Math.abs(i - 10 - n), 1) * i;
    }
    // Calculate module 11 for the calculated digit.
    d = 11 - sum % 11;
    // Case 10 replaces with 0.
    d = d <= 9 ? d : 0;
    // False when not matching calculated digit with check.
    if (parseInt(cpf.substr(9 + n, 1), 10) !== d) {
      return false;
    }
  }
  return true;
};
String.prototype.isCNPJ = function () {
  'use strict';
  // Keep only numbers, inserts leading zeros ensuring correct size.
  var cnpj = this.numbers().pad(14),
    valid = true,
    sum,
    i,
    d;
  // Ignore false positives when only repeating single number.
  if (/^(\d)\1+$/.test(cnpj)) {
    return false;
  }
  // Interaction in each group of multipliers.
  ['543298765432', '6543298765432'].forEach(function (f, n) {
    sum = 0;
    // Multiplies each factor by its position in the interaction accumulating the sum.
    for (i = 0; i < f.length; i += 1) {
      sum += cnpj.substr(i, 1) * f.substr(i, 1);
    }
    // Calculate module 11 for the calculated digit.
    d = 11 - sum % 11;
    // Case 10 replaces with 0.
    d = d <= 9 ? d : 0;
    // False when not matching calculated digit with check.
    if (parseInt(cnpj.substr(12 + n, 1), 10) !== d) {
      valid = false;
    }
  });
  return valid;
};