Generate DNI/NIF for Spain and Portugal, in javascript

dni_portugal.js

//credit : https://github.com/asmarques/pt-id  

function pad(value, length) {
  var result = value + '';

  while (result.length < length) {
    result = '0' + result;
  }

  return result;
}

function checkDigit(value) {
  var sum = 0;
  var len = value.length;

  for (var i = 0; i < len; i++) {
    sum += value[i] * (len + 1 - i);
  }

  var mod = sum % 11;
  return '' + ((mod === 0 || mod === 1) ? 0 : 11 - mod);
}
function generate(prefix) {
  var value = pad(Math.floor(Math.random() * 99999999), 8);

  if (prefix) {
    value = prefix + value.slice(prefix.length, value.length);
  }

  return value + checkDigit(value);
}
// personal =  1,2,3
//company = 5

generate('1');  

dni_spain.js

//credit : https://gist.github.com/THuRStoN/9468324

function formatNumberLength(num, length) {
  var r = "" + num;
  while ( r.length < length ) {
    r = "0" + r;
  }
  return r;
}

function charDNI(dni) {
  var chain = "TRWAGMYFPDXBNJZSQVHLCKET";
  var pos = dni % 23;
  var letter = chain.substring( pos, pos + 1 );
  return letter;
}

function rand_dni() {
  num = Math.floor( ( Math.random() * 100000000 ) );
  sNum = formatNumberLength( num, 8 );
  return sNum + charDNI( sNum );
}

rand_dni();