55 lines
1.5 KiB
JavaScript
55 lines
1.5 KiB
JavaScript
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import assertString from './util/assertString';
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var isin = /^[A-Z]{2}[0-9A-Z]{9}[0-9]$/;
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// this link details how the check digit is calculated:
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// https://www.isin.org/isin-format/. it is a little bit
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// odd in that it works with digits, not numbers. in order
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// to make only one pass through the ISIN characters, the
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// each alpha character is handled as 2 characters within
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// the loop.
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export default function isISIN(str) {
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assertString(str);
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if (!isin.test(str)) {
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return false;
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}
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var _double = true;
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var sum = 0;
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// convert values
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for (var i = str.length - 2; i >= 0; i--) {
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if (str[i] >= 'A' && str[i] <= 'Z') {
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var value = str[i].charCodeAt(0) - 55;
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var lo = value % 10;
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var hi = Math.trunc(value / 10);
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// letters have two digits, so handle the low order
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// and high order digits separately.
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for (var _i = 0, _arr = [lo, hi]; _i < _arr.length; _i++) {
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var digit = _arr[_i];
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if (_double) {
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if (digit >= 5) {
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sum += 1 + (digit - 5) * 2;
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} else {
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sum += digit * 2;
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}
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} else {
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sum += digit;
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}
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_double = !_double;
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}
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} else {
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var _digit = str[i].charCodeAt(0) - '0'.charCodeAt(0);
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if (_double) {
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if (_digit >= 5) {
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sum += 1 + (_digit - 5) * 2;
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} else {
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sum += _digit * 2;
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}
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} else {
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sum += _digit;
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}
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_double = !_double;
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}
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}
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var check = Math.trunc((sum + 9) / 10) * 10 - sum;
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return +str[str.length - 1] === check;
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}
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