From bc3a655f5cbfe3b4edb94c6084f62e95806ea6de Mon Sep 17 00:00:00 2001
From: xobotyi <xog3@yandex.ru>
Date: Sat, 17 Apr 2021 00:22:04 +0300
Subject: [PATCH] feat: useUpdateEffect hook

---
 src/useUpdateEffect.ts             | 14 ++++++++++
 tests/dom/useUpdateEffect.test.ts  | 43 ++++++++++++++++++++++++++++++
 tests/ssr/useMountEffect.test.ts   |  3 +--
 tests/ssr/useUnmountEffect.test.ts |  3 +--
 tests/ssr/useUpdateEffect.test.ts  | 12 +++++++++
 5 files changed, 71 insertions(+), 4 deletions(-)
 create mode 100644 src/useUpdateEffect.ts
 create mode 100644 tests/dom/useUpdateEffect.test.ts
 create mode 100644 tests/ssr/useUpdateEffect.test.ts

diff --git a/src/useUpdateEffect.ts b/src/useUpdateEffect.ts
new file mode 100644
index 000000000..c26c7698f
--- /dev/null
+++ b/src/useUpdateEffect.ts
@@ -0,0 +1,14 @@
+import { DependencyList, EffectCallback, useEffect } from 'react';
+import { useFirstMountState } from './useFirstMountState';
+
+export function useUpdateEffect(effect: EffectCallback, deps?: DependencyList): void {
+  const isFirstMount = useFirstMountState();
+
+  // eslint-disable-next-line consistent-return
+  useEffect(() => {
+    if (!isFirstMount) {
+      return effect();
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, deps);
+}
diff --git a/tests/dom/useUpdateEffect.test.ts b/tests/dom/useUpdateEffect.test.ts
new file mode 100644
index 000000000..9f8561de5
--- /dev/null
+++ b/tests/dom/useUpdateEffect.test.ts
@@ -0,0 +1,43 @@
+import { renderHook } from '@testing-library/react-hooks/dom';
+import { useUpdateEffect } from '../../src/useUpdateEffect';
+
+describe('useUpdateEffect', () => {
+  it('should call effector only on updates (after first render)', () => {
+    const spy = jest.fn();
+
+    const { rerender, unmount } = renderHook(() => useUpdateEffect(spy));
+
+    expect(spy).toHaveBeenCalledTimes(0);
+
+    rerender();
+    expect(spy).toHaveBeenCalledTimes(1);
+
+    rerender();
+    expect(spy).toHaveBeenCalledTimes(2);
+
+    unmount();
+    expect(spy).toHaveBeenCalledTimes(2);
+  });
+
+  it('should accept dependencies as useEffect', () => {
+    const spy = jest.fn();
+
+    const { rerender, unmount } = renderHook(({ deps }) => useUpdateEffect(spy, deps), {
+      initialProps: { deps: [1, 2, 3] },
+    });
+
+    expect(spy).toHaveBeenCalledTimes(0);
+
+    rerender();
+    expect(spy).toHaveBeenCalledTimes(0);
+
+    rerender({ deps: [1, 2, 4] });
+    expect(spy).toHaveBeenCalledTimes(1);
+
+    rerender({ deps: [1, 2, 4] });
+    expect(spy).toHaveBeenCalledTimes(1);
+
+    unmount();
+    expect(spy).toHaveBeenCalledTimes(1);
+  });
+});
diff --git a/tests/ssr/useMountEffect.test.ts b/tests/ssr/useMountEffect.test.ts
index c81acaf4a..ea01bf113 100644
--- a/tests/ssr/useMountEffect.test.ts
+++ b/tests/ssr/useMountEffect.test.ts
@@ -5,9 +5,8 @@ describe('useMountEffect', () => {
   it('should call effector only on first render', () => {
     const spy = jest.fn();
 
-    const { result } = renderHook(() => useMountEffect(spy));
+    renderHook(() => useMountEffect(spy));
 
-    expect(result.current).toBe(undefined);
     expect(spy).toHaveBeenCalledTimes(0);
   });
 });
diff --git a/tests/ssr/useUnmountEffect.test.ts b/tests/ssr/useUnmountEffect.test.ts
index 08fe3dad5..b978f022a 100644
--- a/tests/ssr/useUnmountEffect.test.ts
+++ b/tests/ssr/useUnmountEffect.test.ts
@@ -5,9 +5,8 @@ describe('useUnmountEffect', () => {
   it('should call effector only when component unmounted', () => {
     const spy = jest.fn();
 
-    const { result } = renderHook(() => useUnmountEffect(spy));
+    renderHook(() => useUnmountEffect(spy));
 
-    expect(result.current).toBe(undefined);
     expect(spy).toHaveBeenCalledTimes(0);
   });
 });
diff --git a/tests/ssr/useUpdateEffect.test.ts b/tests/ssr/useUpdateEffect.test.ts
new file mode 100644
index 000000000..2e45f48ed
--- /dev/null
+++ b/tests/ssr/useUpdateEffect.test.ts
@@ -0,0 +1,12 @@
+import { renderHook } from '@testing-library/react-hooks/server';
+import { useUpdateEffect } from '../../src/useUpdateEffect';
+
+describe('useUpdateEffect', () => {
+  it('should not call effector on mount', () => {
+    const spy = jest.fn();
+
+    renderHook(() => useUpdateEffect(spy));
+
+    expect(spy).toHaveBeenCalledTimes(0);
+  });
+});