PESEL

 ( National Identification Numbers ) 

PESEL () is the national identification number used in Poland since 1979. The number is 11 digits long, identifies exactly one person, and cannot be changed once assigned, except in specific situations (such as gender reassignment).

The PESEL number is mandatory for all permanent residents of Poland and for temporary residents living in Poland for over 2 months. After 1 March 2015, applicants for a Polish passport without a PESEL number need to apply for PESEL prior to passport application. Otherwise, without a PESEL number, passport applications and fingerprints cannot be taken.

The PESEL system was originally designed by the communist government of the Polish People's Republic to trace personal information about its citizens. It is a direct offshoot from the previous system, Magister, which was designed to trace and record data about all individuals with a university degree.

A×1 + B×3 + C×7 + D×9 + E×1 + F×3 + G×7 + H×9 + I×1 + J×3

The checksum is the last digit of result of the above expression subtracted from 10. If this last digit is 0, then the checksum is 0.

If the result of the last operation is not equal to the last digit (K) of a given PESEL, then the PESEL is incorrect. This system works reliably well for catching one-digit mistakes and digit swaps.

The last digit of the result (217 modulo 10): 7

The last digit is not 0; the checksum is 10 − 7 = 3

3 is not equal to the last digit of the PESEL, which is 1; the PESEL number is not valid. A valid PESEL would be 12345678903.

   if (pesel.length !== 11)
       return false;
     

   const arr = pesel.split("");
   const multipliers = [1, 3, 7, 9];
   let sum = 0;
     

   for (let i = 0; i < arr.length - 1; i++) {
       sum += Number(arr[i]) * multipliers[i % 4];
   }
     

   const modulo = sum % 10;
   const lastD = Number(pesel[10]);
     

   return lastD === (10 - modulo) % 10;