From e74939ab0fde422e2c4327ad3fb26053f5c68dad Mon Sep 17 00:00:00 2001
From: iamnathanj <nate.jacobs@shopify.com>
Date: Thu, 3 Nov 2022 21:08:12 +0000
Subject: [PATCH 1/4] fix: scrollable calls onScrolledToBottom only when
 container is overflowing

---
 polaris-react/src/components/Scrollable/Scrollable.tsx | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/polaris-react/src/components/Scrollable/Scrollable.tsx b/polaris-react/src/components/Scrollable/Scrollable.tsx
index 0edb4ab38b4..6d92c4f79ed 100644
--- a/polaris-react/src/components/Scrollable/Scrollable.tsx
+++ b/polaris-react/src/components/Scrollable/Scrollable.tsx
@@ -67,6 +67,7 @@ export function Scrollable({
 
     requestAnimationFrame(() => {
       const {scrollTop, clientHeight, scrollHeight} = currentScrollArea;
+      const canScroll = Boolean(scrollHeight > clientHeight);
       const isBelowTopOfScroll = Boolean(scrollTop > 0);
       const isAtBottomOfScroll = Boolean(
         scrollTop + clientHeight >= scrollHeight - LOW_RES_BUFFER,
@@ -75,7 +76,7 @@ export function Scrollable({
       setTopShadow(isBelowTopOfScroll);
       setBottomShadow(!isAtBottomOfScroll);
 
-      if (isAtBottomOfScroll && onScrolledToBottom) {
+      if (canScroll && isAtBottomOfScroll && onScrolledToBottom) {
         onScrolledToBottom();
       }
     });

From 6b60a0e85e5bfa0aff20187556ea0daaca684d90 Mon Sep 17 00:00:00 2001
From: iamnathanj <nate.jacobs@shopify.com>
Date: Fri, 4 Nov 2022 11:24:20 -0400
Subject: [PATCH 2/4] add tests for onScrolledToBottom

---
 .../Scrollable/tests/Scrollable.test.tsx      | 57 +++++++++++++++++++
 polaris-react/tests/setup/tests.ts            |  5 ++
 2 files changed, 62 insertions(+)

diff --git a/polaris-react/src/components/Scrollable/tests/Scrollable.test.tsx b/polaris-react/src/components/Scrollable/tests/Scrollable.test.tsx
index 5572dbcb86a..480a0bba49d 100644
--- a/polaris-react/src/components/Scrollable/tests/Scrollable.test.tsx
+++ b/polaris-react/src/components/Scrollable/tests/Scrollable.test.tsx
@@ -3,6 +3,7 @@ import {mountWithApp} from 'tests/utilities';
 
 import {Scrollable} from '../Scrollable';
 import {ScrollableContext} from '../context';
+import type {ScrollableProps} from '../Scrollable';
 
 describe('<Scrollable />', () => {
   it('mounts', () => {
@@ -71,4 +72,60 @@ describe('<Scrollable />', () => {
       tabIndex: 0,
     });
   });
+
+  it('calls onScrolledToBottom when scrolled to bottom', () => {
+    const onScrolledToBottom = jest.fn();
+
+    const scrollArea = mountWithApp(
+      <Scrollable
+        data-test-id="scroll-element"
+        onScrolledToBottom={onScrolledToBottom}
+      >
+        <p>Hello</p>
+      </Scrollable>,
+    );
+
+    const scrollNode = scrollArea.find('div', {
+      'data-test-id': 'scroll-element',
+    } as ScrollableProps)?.domNode!;
+
+    // defineProperty needed to assign values to readonly node properties
+    Object.defineProperty(scrollNode, 'clientHeight', {get: () => 0});
+    Object.defineProperty(scrollNode, 'scrollHeight', {get: () => 10});
+    Object.defineProperty(scrollNode, 'scrollTop', {get: () => 10});
+
+    scrollArea.act(() => {
+      scrollNode.dispatchEvent(new Event('scroll'));
+    });
+
+    expect(onScrolledToBottom).toHaveBeenCalledTimes(1);
+  });
+
+  it(`doesn't call onScrolledToBottom when the scroll area is not overflowing`, () => {
+    const onScrolledToBottom = jest.fn();
+
+    const scrollArea = mountWithApp(
+      <Scrollable
+        data-test-id="scroll-element"
+        onScrolledToBottom={onScrolledToBottom}
+      >
+        <p>Hello</p>
+      </Scrollable>,
+    );
+
+    const scrollNode = scrollArea.find('div', {
+      'data-test-id': 'scroll-element',
+    } as ScrollableProps)?.domNode!;
+
+    // defineProperty needed to assign values to readonly node properties
+    Object.defineProperty(scrollNode, 'clientHeight', {get: () => 10});
+    Object.defineProperty(scrollNode, 'scrollHeight', {get: () => 10});
+    Object.defineProperty(scrollNode, 'scrollTop', {get: () => 10});
+
+    scrollArea.act(() => {
+      scrollNode.dispatchEvent(new Event('scroll'));
+    });
+
+    expect(onScrolledToBottom).not.toHaveBeenCalled();
+  });
 });
diff --git a/polaris-react/tests/setup/tests.ts b/polaris-react/tests/setup/tests.ts
index a18d7daf9e8..489a2a0b02c 100644
--- a/polaris-react/tests/setup/tests.ts
+++ b/polaris-react/tests/setup/tests.ts
@@ -6,3 +6,8 @@ import './matchers';
 afterEach(() => {
   destroyAll();
 });
+
+globalThis.requestAnimationFrame = (cb) => {
+  cb(Date.now());
+  return Math.random();
+};

From 5f7cdeeafc599e8c858b34d7759f640e5dcb702c Mon Sep 17 00:00:00 2001
From: iamnathanj <nate.jacobs@shopify.com>
Date: Fri, 4 Nov 2022 12:26:39 -0400
Subject: [PATCH 3/4] mock rAF locally in new tests

---
 .../Scrollable/tests/Scrollable.test.tsx          | 15 +++++++++++++++
 polaris-react/tests/setup/tests.ts                |  5 -----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/polaris-react/src/components/Scrollable/tests/Scrollable.test.tsx b/polaris-react/src/components/Scrollable/tests/Scrollable.test.tsx
index 480a0bba49d..c04bdc41de3 100644
--- a/polaris-react/src/components/Scrollable/tests/Scrollable.test.tsx
+++ b/polaris-react/src/components/Scrollable/tests/Scrollable.test.tsx
@@ -6,6 +6,21 @@ import {ScrollableContext} from '../context';
 import type {ScrollableProps} from '../Scrollable';
 
 describe('<Scrollable />', () => {
+  let rafSpy: jest.SpyInstance;
+
+  beforeAll(() => {
+    rafSpy = jest
+      .spyOn(window, 'requestAnimationFrame')
+      .mockImplementation((cb) => {
+        cb(Date.now());
+        return Math.random();
+      });
+  });
+
+  afterAll(() => {
+    rafSpy.mockRestore();
+  });
+
   it('mounts', () => {
     const scrollable = mountWithApp(<Scrollable />);
     expect(scrollable).toBeDefined();
diff --git a/polaris-react/tests/setup/tests.ts b/polaris-react/tests/setup/tests.ts
index 489a2a0b02c..a18d7daf9e8 100644
--- a/polaris-react/tests/setup/tests.ts
+++ b/polaris-react/tests/setup/tests.ts
@@ -6,8 +6,3 @@ import './matchers';
 afterEach(() => {
   destroyAll();
 });
-
-globalThis.requestAnimationFrame = (cb) => {
-  cb(Date.now());
-  return Math.random();
-};

From b8942ce5a07b8a3bf5077f7024b6bd0111bd5134 Mon Sep 17 00:00:00 2001
From: iamnathanj <nate.jacobs@shopify.com>
Date: Fri, 4 Nov 2022 14:40:28 -0400
Subject: [PATCH 4/4] add changeset

---
 .changeset/thick-clocks-applaud.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/thick-clocks-applaud.md

diff --git a/.changeset/thick-clocks-applaud.md b/.changeset/thick-clocks-applaud.md
new file mode 100644
index 00000000000..676b4fdbf64
--- /dev/null
+++ b/.changeset/thick-clocks-applaud.md
@@ -0,0 +1,5 @@
+---
+'@shopify/polaris': patch
+---
+
+Fixed Scrollable component to match existing onScrolledToBottom logic