Add string utility function: isValidSwissSocialSecurityNumber

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- `isValidSwissSocialSecurityNumber` 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, isValidSwissSocialSecurityNumber } from "./string";
 
 describe("string tests", () => {
   test.each([
@@ -120,4 +120,18 @@ 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],
+    ["7561234567891", false],
+    ["7569217076985", true],
+    ["756.9217.0769.85", true],
+    ["756..9217.0769.85", false],
+    ["756.1234.5678.91", false],
+    ["test756.9217.0769.85", false],
+    ["7.56..9217...0769.85", false],
+  ])("check if the social insurance number is valid or not", (ahvNumber, expected) => {
+    expect(isValidSwissSocialSecurityNumber(ahvNumber)).toBe(expected);
+  });
 });

src/lib/string.ts

@@ -64,3 +64,56 @@ export function truncate(value: string | undefined, maxLength: number, suffix =
 
   return `${value.slice(0, maxLength)}${suffix}`;
 }
+
+/**
+ * Validation of social insurance number with checking the checksum
+ * Validation according to https://www.sozialversicherungsnummer.ch/aufbau-neu.htm
+ * @param socialInsuranceNumber The social insurance number to check
+ * Must be in one of the following formats:
+ * - "756.XXXX.XXXX.XX" with dots as seperators
+ * - "756XXXXXXXXXX" with digits only
+ * @returns The result if the social insurance number is valid or not
+ */
+export function isValidSwissSocialSecurityNumber(socialInsuranceNumber: string): boolean {
+  if (isNullOrWhitespace(socialInsuranceNumber)) {
+    return false;
+  }
+
+  const socialInsuranceNumberWithDots = new RegExp(/^756.?\d{4}.?\d{4}.?\d{2}$/);
+
+  if (!socialInsuranceNumberWithDots.test(socialInsuranceNumber)) {
+    return false;
+  }
+
+  /**
+   * Validates a Swiss social security number (AHV number).
+   *
+   * Validation steps:
+   * - The number must start with 756, be 13 digits long and follow one of the accepted formats:
+   *   - "756.XXXX.XXXX.XX" or "756XXXXXXXXXX".
+   * - Remove dots → 13 digits remain.
+   * - The last digit is the check digit.
+   * - To calculate the check digit:
+   *   - Take the first 12 digits and reverse them.
+   *   - Multiply digits at even positions by 3, and digits at odd positions by 1.
+   *   - Sum all results.
+   *   - Look at the last digit of the sum (sum % 10).
+   *   - The check digit is the value needed to reach the next multiple of 10.
+   * - The number is valid if this check digit matches the last digit.
+   */
+
+  const compactNumber = socialInsuranceNumber.replaceAll(".", "");
+  const digits = compactNumber.slice(0, -1);
+  const reversedDigits = [...digits].reverse().join("");
+  const reversedDigitsArray = [...reversedDigits];
+
+  let sum = 0;
+  for (const [i, element] of reversedDigitsArray.entries()) {
+    sum += i % 2 === 0 ? Number(element) * 3 : Number(element) * 1;
+  }
+
+  const checksum = (10 - (sum % 10)) % 10;
+  const checknumber = Number.parseInt(compactNumber.slice(-1));
+
+  return checksum === checknumber;
+}