MortgageRegister calculate and verify checksum

mortgage_register_checksum.js

// https://ekw.ms.gov.pl/

class MortgageRegister {
  
  static check(str) {
    const m = str.match(/([A-Z0-9]{4}\/[0-9]{8})\/([0-9])/);
    if (m) {
      return this.checksum(m[1]) === +m[2];
    }
    return false;
  }
  
  static checksum(str) {
    const a = '0123456789XABCDEFGHIJKLMNOPRSTUWYZ';
    return (
      (str.toUpperCase().match(/[a-z0-9]/gi) || [])
      .map((c, i) => a.indexOf(c) * [1, 3, 7][i%3])
      .reduce((a, n) => a + n, 0)
    ) % 10;
  }

};


console.log([
	MortgageRegister.check('WL1A/00272852/9'),
	MortgageRegister.checksum('WL1A/00272852')
]);