Turkish National Identity Validation • TC Kimlik Numarası Doğrulama

IsNationalIdentity.ts

/**
 * Returns true if the given string is a valid Turkish national identity number.
 *
 * @remarks
 * This implementation uses the algorithm described on the Wikipedia page
 * "Turkish Identification Number".
 * @param value - The string to check.
 * @returns True if the string is a valid Turkish national identity number, false otherwise.
 */
const IsNationalIdentity = (value: string): boolean => {
  if (
    value == null ||
    typeof value !== 'string' ||
    value.length !== 11 ||
    /\D/.test(value)
  ) {
    return false;
  }

  let sum = 0;
  let sumOdd = 0;
  let sumEven = 0;
  let c1 = 0;
  let c2 = 0;

  for (let i = 0; i < value.length; i++) {
    const e = Number.parseInt(value[i]);

    if (i === 9) {
      c1 = e;
    } else if (i === 10) {
      c2 = e;
    } else {
      sum += e;

      if (i % 2 === 0) {
        sumEven += e;
      } else {
        sumOdd += e;
      }
    }
  }

  return c1 === (sumEven * 7 - sumOdd) % 10 && c2 === (sum + c1) % 10;
};