Validierung der deutschen Steueridentifikationsnummer

StIdNr-Validierung.js

number = '9132456781'.split('');

validation = number.pop();
var n = 11,
    m = 10,
    product = m,
    sum     = 0;
console.log("StIdNr: %s, validation: %s", number.join(''),validation);
for (var i in number) {
  var c = parseInt(number[i], m);
  sum = (c + product) % m;
  if (sum === 0) sum = m;
  product = (2*sum) % n;
  console.log("%d: %d, %d, %d", i, c, sum, product);
}
var pz = n - product;
if (pz == m) pz = 0;

console.log("Checksum = %d, original=%s", pz, validation);