From d122f9f2e4c7ed4adea89f4aeeaaefaf5fe97e5b Mon Sep 17 00:00:00 2001
From: Daniele Debernardi <daniele.debernardi@neolution.ch>
Date: Wed, 8 Oct 2025 14:25:13 +0200
Subject: [PATCH 1/2] Adds useConstructor hook

Introduces a `useConstructor` hook that executes a provided callback only once during the component's lifecycle, similar to a constructor.

This ensures that initialization logic is performed only once, even after re-renders or component remounts. Includes thorough tests to confirm the hook's behavior in different scenarios.
---
 cypress/component/useConstructor.cy.tsx | 65 +++++++++++++++++++++++++
 src/index.ts                            |  1 +
 src/lib/hooks/useConstructor.ts         | 15 ++++++
 3 files changed, 81 insertions(+)
 create mode 100644 cypress/component/useConstructor.cy.tsx
 create mode 100644 src/lib/hooks/useConstructor.ts

diff --git a/cypress/component/useConstructor.cy.tsx b/cypress/component/useConstructor.cy.tsx
new file mode 100644
index 0000000..429618f
--- /dev/null
+++ b/cypress/component/useConstructor.cy.tsx
@@ -0,0 +1,65 @@
+import React, { useState } from "react";
+import { useConstructor } from "../../src/lib/hooks/useConstructor";
+
+describe("useConstructor", () => {
+  it("calls the callback exactly once per mount, even after re-renders", () => {
+    const initSpy = cy.spy().as("initSpy");
+
+    const TestComponent: React.FC = () => {
+      const [count, setCount] = useState(0);
+      useConstructor(() => {
+        initSpy();
+      });
+
+      return (
+        <div>
+          <span data-cy="count">{count}</span>
+          <button onClick={() => setCount((c) => c + 1)}>Increment</button>
+        </div>
+      );
+    };
+
+    // Turn off StrictMode as it will double‑invoke mount logic
+    cy.mount(<TestComponent />, { strict: false });
+
+    cy.get("@initSpy").should("have.been.calledOnce");
+
+    // Cause several re-renders
+    cy.contains("Increment").click().click().click();
+    cy.get("[data-cy='count']").should("have.text", "3");
+
+    cy.get("@initSpy").should("have.been.calledOnce");
+  });
+
+  it("runs again after an unmount/remount (new instance)", () => {
+    const initSpy = cy.spy().as("initSpy");
+
+    const Wrapper: React.FC = () => {
+      const [show, setShow] = useState(true);
+      return (
+        <div>
+          <button onClick={() => setShow((s) => !s)}>Toggle</button>
+          {show && <Child />}
+        </div>
+      );
+    };
+
+    const Child: React.FC = () => {
+      useConstructor(() => initSpy());
+      return <div data-cy="child">Child</div>;
+    };
+
+    // Turn off StrictMode as it will double‑invoke mount logic
+    cy.mount(<Wrapper />, { strict: false });
+
+    cy.get("@initSpy").should("have.been.calledOnce");
+
+    cy.contains("Toggle").click(); // unmount
+    cy.get("[data-cy='child']").should("not.exist");
+
+    cy.contains("Toggle").click(); // remount
+    cy.get("[data-cy='child']").should("exist");
+
+    cy.get("@initSpy").should("have.callCount", 2);
+  });
+});
diff --git a/src/index.ts b/src/index.ts
index 7d1517e..e89e661 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1 +1,2 @@
+export * from "./lib/hooks/useConstructor";
 export * from "./lib/hooks/useHelloWorld";
diff --git a/src/lib/hooks/useConstructor.ts b/src/lib/hooks/useConstructor.ts
new file mode 100644
index 0000000..1a19f88
--- /dev/null
+++ b/src/lib/hooks/useConstructor.ts
@@ -0,0 +1,15 @@
+import { useRef } from "react";
+
+/**
+ * Custom hook that runs the provided callback only once during the component's lifecycle.
+ * @param callback - Function to be executed once on component mount.
+ */
+const useConstructor = (callback: () => void) => {
+  const calledRef = useRef(false);
+  if (!calledRef.current) {
+    callback();
+    calledRef.current = true;
+  }
+};
+
+export { useConstructor };

From 8ce9787062d0780c549d01af3078506b17cacc15 Mon Sep 17 00:00:00 2001
From: Daniele Debernardi <daniele.debernardi@neolution.ch>
Date: Wed, 8 Oct 2025 14:28:27 +0200
Subject: [PATCH 2/2] add changelog

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

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 11bddf3..b1dd472 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,3 +6,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+
+### Added
+
+- `useConstructor` hook that executes a provided callback only once during the component's lifecycle, similar to a constructor.