Add utility function isValidSwissIbanNumber

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- `isValidSwissIbanNumber` string utility function
+
 ## [2.0.0] - 2025-07-29
 
 ### Added

src/lib/string.spec.ts

@@ -1,4 +1,4 @@
-import { isNullOrEmpty, isNullOrWhitespace, capitalize, uncapitalize, truncate } from "./string";
+import { isNullOrEmpty, isNullOrWhitespace, capitalize, uncapitalize, truncate, isValidSwissIbanNumber } from "./string";
 
 describe("string tests", () => {
   test.each([
@@ -120,4 +120,16 @@ describe("string tests", () => {
   ])("truncate without suffix parameter", (value, maxLength, expected) => {
     expect(truncate(value, maxLength)).toBe(expected);
   });
+
+  test.each([
+    [null as unknown as string, false],
+    [undefined as unknown as string, false],
+    ["CH9300762011623852957", true],
+    ["CH93 0000 0000 0000 0000 1", false],
+    ["ch93 0076 2011 6238 5295 7", false],
+    ["DE93 0076 2011 6238 5295 7", false],
+    ["CH93 0076 2011 6238 5295 7", true],
+  ])("Is IBAN valid", (unformattedIbanNumber, expected) => {
+    expect(isValidSwissIbanNumber(unformattedIbanNumber)).toBe(expected);
+  });
 });

src/lib/string.ts

@@ -64,3 +64,33 @@ export function truncate(value: string | undefined, maxLength: number, suffix =
 
   return `${value.slice(0, maxLength)}${suffix}`;
 }
+
+/**
+ * Checks if the provided string is a valid Swiss IBAN number
+ * @param iBanNumber The provided IBAN number to check
+ * @returns The result of the IBAN number check
+ */
+export function isValidSwissIbanNumber(iBanNumber: string): boolean {
+  if (!isNullOrEmpty(iBanNumber)) {
+    const compactIban = iBanNumber.replaceAll(/\s+/g, "");
+    if (!/^CH\d{19}$/.test(compactIban)) return false;
+    const rearrangedIban = compactIban.slice(4) + compactIban.slice(0, 4);
+
+    const numericStr = Array.from(rearrangedIban, (ch) => {
+      if (/[A-Z]/.test(ch)) {
+        const code = ch.codePointAt(0);
+        // code is never undefined!
+        return (code! - 55).toString();
+      }
+      return ch;
+    }).join("");
+
+    let restOfCalculation = 0;
+    for (const digit of numericStr) {
+      restOfCalculation = (restOfCalculation * 10 + Number(digit)) % 97;
+    }
+
+    return restOfCalculation === 1;
+  }
+  return false;
+}