DistroHard/node_modules/validator/es/lib/isISIN.js

import assertString from './util/assertString';
var isin = /^[A-Z]{2}[0-9A-Z]{9}[0-9]$/; // this link details how the check digit is calculated:
// https://www.isin.org/isin-format/. it is a little bit
// odd in that it works with digits, not numbers. in order
// to make only one pass through the ISIN characters, the
// each alpha character is handled as 2 characters within
// the loop.

export default function isISIN(str) {
  assertString(str);

  if (!isin.test(str)) {
    return false;
  }

  var _double = true;
  var sum = 0; // convert values

  for (var i = str.length - 2; i >= 0; i--) {
    if (str[i] >= 'A' && str[i] <= 'Z') {
      var value = str[i].charCodeAt(0) - 55;
      var lo = value % 10;
      var hi = Math.trunc(value / 10); // letters have two digits, so handle the low order
      // and high order digits separately.

      for (var _i = 0, _arr = [lo, hi]; _i < _arr.length; _i++) {
        var digit = _arr[_i];

        if (_double) {
          if (digit >= 5) {
            sum += 1 + (digit - 5) * 2;
          } else {
            sum += digit * 2;
          }
        } else {
          sum += digit;
        }

        _double = !_double;
      }
    } else {
      var _digit = str[i].charCodeAt(0) - '0'.charCodeAt(0);

      if (_double) {
        if (_digit >= 5) {
          sum += 1 + (_digit - 5) * 2;
        } else {
          sum += _digit * 2;
        }
      } else {
        sum += _digit;
      }

      _double = !_double;
    }
  }

  var check = Math.trunc((sum + 9) / 10) * 10 - sum;
  return +str[str.length - 1] === check;
}