From af3ff454e2b84660f8ea0ac3e428c52129e2a0a8 Mon Sep 17 00:00:00 2001
From: rrbharath <ryanrbharath@gmail.com>
Date: Mon, 8 Jun 2026 19:27:26 -0400
Subject: [PATCH] feat(isISMN): add validator for isISMN

---
 README.md                      |  2 ++
 src/index.js                   |  2 ++
 src/lib/isISMN.js              | 27 +++++++++++++++++++++++++
 test/validators/isISMN.test.js | 37 ++++++++++++++++++++++++++++++++++
 4 files changed, 68 insertions(+)
 create mode 100644 src/lib/isISMN.js
 create mode 100644 test/validators/isISMN.test.js

diff --git a/README.md b/README.md
index 8ef42fd79..2d99bd4bb 100644
--- a/README.md
+++ b/README.md
@@ -127,6 +127,7 @@ Validator                               | Description
 **isIPRange(str [, version])**          | check if the string is an IP Range (version 4 or 6).
 **isISBN(str [, options])**             | check if the string is an [ISBN][ISBN].<br/><br/>`options` is an object that has no default.<br/>**Options:**<br/>`version`: ISBN version to compare to. Accepted values are '10' and '13'. If none provided, both will be tested.
 **isISIN(str)**                         | check if the string is an [ISIN][ISIN] (stock/security identifier).
+**isISMN(str)**                         | check if the string is an [ISMN][ISMN]. Supports the modern 13-digit format beginning with `979-0` and the legacy 10-character format beginning with `M`.
 **isISO6346(str)**                      | check if the string is a valid [ISO 6346](https://en.wikipedia.org/wiki/ISO_6346) shipping container identification.
 **isISO6391(str)**                      | check if the string is a valid [ISO 639-1][ISO 639-1] language code.
 **isISO8601(str [, options])**          | check if the string is a valid [ISO 8601][ISO 8601] date. <br/>`options` is an object which defaults to `{ strict: false, strictSeparator: false }`. If `strict` is true, date strings with invalid dates like `2009-02-29` will be invalid. If `strictSeparator` is true, date strings with date and time separated by anything other than a T will be invalid.
@@ -251,6 +252,7 @@ This project is licensed under the [MIT](LICENSE). See the [LICENSE](LICENSE) fi
 [IMEI]: https://en.wikipedia.org/wiki/International_Mobile_Equipment_Identity
 [ISBN]: https://en.wikipedia.org/wiki/ISBN
 [ISIN]: https://en.wikipedia.org/wiki/International_Securities_Identification_Number
+[ISMN]: https://ismn-international.org/ismn/the-ismn/
 [ISO 639-1]: https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes
 [ISO 8601]: https://en.wikipedia.org/wiki/ISO_8601
 [ISO 15924]: https://en.wikipedia.org/wiki/ISO_15924
diff --git a/src/index.js b/src/index.js
index 3700cbd6c..92272bca8 100644
--- a/src/index.js
+++ b/src/index.js
@@ -79,6 +79,7 @@ import isIdentityCard from './lib/isIdentityCard';
 import isEAN from './lib/isEAN';
 import isISIN from './lib/isISIN';
 import isISBN from './lib/isISBN';
+import isISMN from './lib/isISMN';
 import isISSN from './lib/isISSN';
 import isTaxID from './lib/isTaxID';
 
@@ -200,6 +201,7 @@ const validator = {
   isEAN,
   isISIN,
   isISBN,
+  isISMN,
   isISSN,
   isMobilePhone,
   isMobilePhoneLocales,
diff --git a/src/lib/isISMN.js b/src/lib/isISMN.js
new file mode 100644
index 000000000..9b0b9a0c1
--- /dev/null
+++ b/src/lib/isISMN.js
@@ -0,0 +1,27 @@
+import assertString from './util/assertString';
+
+const possibleIsmn10 = /^M[0-9]{9}$/;
+const possibleIsmn13 = /^9790[0-9]{9}$/;
+const factor = [1, 3];
+
+function hasValidCheckDigit(ismn) {
+  let checksum = 0;
+
+  for (let i = 0; i < 12; i++) {
+    checksum += factor[i % 2] * Number(ismn.charAt(i));
+  }
+
+  return Number(ismn.charAt(12)) === ((10 - (checksum % 10)) % 10);
+}
+
+export default function isISMN(ismn) {
+  assertString(ismn);
+
+  const sanitizedIsmn = ismn.replace(/[\s-]+/g, '').toUpperCase();
+
+  if (possibleIsmn10.test(sanitizedIsmn)) {
+    return hasValidCheckDigit(`9790${sanitizedIsmn.slice(1)}`);
+  }
+
+  return possibleIsmn13.test(sanitizedIsmn) && hasValidCheckDigit(sanitizedIsmn);
+}
diff --git a/test/validators/isISMN.test.js b/test/validators/isISMN.test.js
new file mode 100644
index 000000000..f17099ee8
--- /dev/null
+++ b/test/validators/isISMN.test.js
@@ -0,0 +1,37 @@
+import test from '../testFunctions';
+
+describe('isISMN', () => {
+  it('should validate ISMNs', () => {
+    test({
+      validator: 'isISMN',
+      valid: [
+        '9790345246805',
+        '979-0-345-24680-5',
+        '979 0 345 24680 5',
+        '9790215901001',
+        '979-0-2159-0100-1',
+        '979 0 2159 0100 1',
+        'M345246805',
+        'M-345-24680-5',
+        'M 345 24680 5',
+        'm-345-24680-5',
+        'M230671187',
+        'M-2306-7118-7',
+      ],
+      invalid: [
+        '9790345246800',
+        '979-0-345-24680-0',
+        '979-1-345-24680-5',
+        '9780345246805',
+        'M345246800',
+        'M-345-24680-0',
+        'M-345-24680-X',
+        'M-345-2468A-5',
+        '979034524680',
+        '97903452468055',
+        'foo',
+        '',
+      ],
+    });
+  });
+});