From 0df70210221b9c1f874c7625597fb08bb650d3b2 Mon Sep 17 00:00:00 2001
From: luke <luca.schmid@neolution.ch>
Date: Thu, 10 Apr 2025 14:52:35 +0200
Subject: [PATCH 1/2] Add getFirstDayOfYear function

---
 src/lib/date.spec.ts | 16 ++++++++++++++++
 src/lib/date.ts      |  9 +++++++++
 2 files changed, 25 insertions(+)

diff --git a/src/lib/date.spec.ts b/src/lib/date.spec.ts
index c942105..71a1393 100644
--- a/src/lib/date.spec.ts
+++ b/src/lib/date.spec.ts
@@ -8,6 +8,7 @@ import {
   getNextBusinessDate,
   getStartOfDay,
   getEndOfDay,
+  getFirstDayOfYear,
   getLastDayOfYear,
 } from "./date";
 
@@ -132,6 +133,21 @@ describe("date tests", () => {
     expect(getEndOfDay(date).getTime()).toBe(expected.getTime());
   });
 
+  test.each([
+    [null as unknown as Date, new Date(Number.NaN)],
+    [undefined as unknown as Date, new Date(Number.NaN)],
+    [42 as unknown as Date, new Date(Number.NaN)],
+    ["test" as unknown as Date, new Date(Number.NaN)],
+  ])("getFirstDayOfYear", (date, expected) => {
+    expect(getFirstDayOfYear(date).getTime()).toBe(expected.getTime());
+  });
+
+  test("getFirstDayOfYear all days", () => {
+    for (let date = new Date(2024, 0, 1); date < new Date(2025, 0, 1); date.setDate(date.getDate() + 1)) {
+      expect(getFirstDayOfYear(date).getTime()).toBe(new Date(2024, 0, 1, 0, 0, 0, 0).getTime());
+    }
+  });
+
   test.each([
     [null as unknown as Date, new Date(Number.NaN)],
     [undefined as unknown as Date, new Date(Number.NaN)],
diff --git a/src/lib/date.ts b/src/lib/date.ts
index c185ca7..8039339 100644
--- a/src/lib/date.ts
+++ b/src/lib/date.ts
@@ -95,6 +95,15 @@ export function getEndOfDay(date: Date): Date {
   return dateIsValid(date) ? endOfDay(date) : new Date(Number.NaN);
 }
 
+/**
+ * Get the first day of a year for the given date
+ * @param date The date
+ * @returns The first day of the date year
+ */
+export function getFirstDayOfYear(date: Date): Date {
+  return dateIsValid(date) ? new Date(date.getFullYear(), 0, 1) : new Date(Number.NaN);
+}
+
 /**
  * Get the last day of a year for the given date
  * @param date The date

From 90e23df0519ebf18427b0218b61f148bb0566f0e Mon Sep 17 00:00:00 2001
From: luke <luca.schmid@neolution.ch>
Date: Thu, 10 Apr 2025 14:57:19 +0200
Subject: [PATCH 2/2] changelog

---
 CHANGELOG.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4995474..9fe5749 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Unnecessary dev-dependencies
 
+### Added
+
+- `getFirstDayOfYear` date utility function
+
 ## [1.2.2] - 2025-04-04
 
 ### Changed