src/node_modules/validator/es/lib/isISBN.js


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import assertString from './util/assertString';
var isbn10Maybe = /^(?:[0-9]{9}X|[0-9]{10})$/;
var isbn13Maybe = /^(?:[0-9]{13})$/;
var factor = [1, 3];
export default function isISBN(str) {
  var version = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : '';
  assertString(str);
  version = String(version);

  if (!version) {
    return isISBN(str, 10) || isISBN(str, 13);
  }

  var sanitized = str.replace(/[\s-]+/g, '');
  var checksum = 0;
  var i;

  if (version === '10') {
    if (!isbn10Maybe.test(sanitized)) {
      return false;
    }

    for (i = 0; i < 9; i++) {
      checksum += (i + 1) * sanitized.charAt(i);
    }

    if (sanitized.charAt(9) === 'X') {
      checksum += 10 * 10;
    } else {
      checksum += 10 * sanitized.charAt(9);
    }

    if (checksum % 11 === 0) {
      return !!sanitized;
    }
  } else if (version === '13') {
    if (!isbn13Maybe.test(sanitized)) {
      return false;
    }

    for (i = 0; i < 12; i++) {
      checksum += factor[i % 2] * sanitized.charAt(i);
    }

    if (sanitized.charAt(12) - (10 - checksum % 10) % 10 === 0) {
      return !!sanitized;
    }
  }

  return false;
}