Function isValidNationalCode

isValidNationalCode(nationalCode: string): boolean
Validates an Iranian national code.

This function checks if the provided national code is a valid 10-digit Iranian national code. It performs a checksum validation to ensure the code is correct.
Parameters
- nationalCode: string
  The national code to validate. It should be a string of 10 digits.
Returns boolean
true if the national code is valid, false otherwise.
Example
```
import isValidNationalCode from './is-valid-national-code';

const validCode = '0025210701';
const invalidCode = '1234567891';

console.log(isValidNationalCode(validCode)); // true or false depending on the checksum
console.log(isValidNationalCode(invalidCode)); // false
```
- Defined in functions/is-valid-national-code/index.ts:21