Fix screen measurement when scrollWidth is a float

.changeset/eleven-doors-count.md

@@ -0,0 +1,5 @@
+---
+'nuka-carousel': patch
+---
+
+Fix screen measurement when scrollWidth is a float

.gitignore

@@ -37,6 +37,7 @@ dist
 types
 yarn-error.log*
 package-lock.json
+coverage
 
 cypress/screenshots
 cypress/videos

packages/nuka/jest.config.js

@@ -1,4 +1,6 @@
 module.exports = {
+  collectCoverage: true,
+  collectCoverageFrom: ['./src/**'],
   moduleNameMapper: {
     '\\.(css|less)$': '<rootDir>/__mocks__/styleMock.js',
   },

packages/nuka/package.json

@@ -17,7 +17,7 @@
     "preversion": "pnpm run check",
     "test": "pnpm run test:unit",
     "test:ci": "pnpm run test:unit:ci",
-    "test:unit": "jest --testPathIgnorePatterns=\\(/es /lib\\)",
+    "test:unit": "jest",
     "test:unit:ci": "pnpm run test:unit",
     "test:unit:watch": "pnpm run test:unit --watchAll",
     "test:storybook": "test-storybook",

packages/nuka/src/hooks/use-measurement.test.tsx

@@ -0,0 +1,140 @@
+/* eslint-disable @typescript-eslint/no-explicit-any */
+import { renderHook } from '@testing-library/react';
+
+import { useMeasurement } from './use-measurement';
+import * as hooks from './use-resize-observer';
+
+const domElement = {} as any;
+jest.spyOn(hooks, 'useResizeObserver').mockImplementation(() => domElement);
+
+describe('useMeasurement', () => {
+  it('return the default values', () => {
+    const { result } = renderHook(() =>
+      useMeasurement({
+        element: { current: null },
+        scrollDistance: 'screen',
+      }),
+    );
+
+    const { totalPages, scrollOffset } = result.current;
+
+    expect(totalPages).toBe(0);
+    expect(scrollOffset).toEqual([]);
+  });
+
+  it('should return measurements for screen', () => {
+    const element = {
+      current: {
+        // this test covers a specific rounding error that can
+        // occur when the scrollWidth/offsetWidth returns a float
+        scrollWidth: 900,
+        offsetWidth: 500,
+        querySelector: () => ({
+          children: [
+            { offsetWidth: 200 },
+            { offsetWidth: 300 },
+            { offsetWidth: 400 },
+          ],
+        }),
+      },
+    } as any;
+
+    const { result } = renderHook(() =>
+      useMeasurement({
+        element,
+        scrollDistance: 'screen',
+      }),
+    );
+
+    const { totalPages, scrollOffset } = result.current;
+
+    expect(totalPages).toBe(2);
+    expect(scrollOffset).toEqual([0, 500]);
+  });
+
+  it('should return measurements for screen with fractional pixels', () => {
+    const element = {
+      current: {
+        // this test covers a specific rounding error that can
+        // occur when the scrollWidth/offsetWidth returns a float
+        scrollWidth: 1720,
+        offsetWidth: 573,
+        querySelector: () => ({
+          children: [
+            { offsetWidth: 573 },
+            { offsetWidth: 573 },
+            { offsetWidth: 573 },
+          ],
+        }),
+      },
+    } as any;
+
+    const { result } = renderHook(() =>
+      useMeasurement({
+        element,
+        scrollDistance: 'screen',
+      }),
+    );
+
+    const { totalPages, scrollOffset } = result.current;
+
+    expect(totalPages).toBe(3);
+    expect(scrollOffset).toEqual([0, 573, 1146]);
+  });
+
+  it('should return measurements for slide distance', () => {
+    const element = {
+      current: {
+        scrollWidth: 900,
+        offsetWidth: 500,
+        querySelector: () => ({
+          children: [
+            { offsetWidth: 200 },
+            { offsetWidth: 300 },
+            { offsetWidth: 400 },
+          ],
+        }),
+      },
+    } as any;
+
+    const { result } = renderHook(() =>
+      useMeasurement({
+        element,
+        scrollDistance: 'slide',
+      }),
+    );
+
+    const { totalPages, scrollOffset } = result.current;
+
+    expect(totalPages).toBe(3);
+    expect(scrollOffset).toEqual([0, 200, 500]);
+  });
+
+  it('should return measurements for numbered distance', () => {
+    const element = {
+      current: {
+        scrollWidth: 900,
+        offsetWidth: 500,
+        querySelector: () => ({
+          children: [
+            { offsetWidth: 200 },
+            { offsetWidth: 300 },
+            { offsetWidth: 400 },
+          ],
+        }),
+      },
+    } as any;
+
+    const { result } = renderHook(() =>
+      useMeasurement({
+        element,
+        scrollDistance: 200,
+      }),
+    );
+
+    const { totalPages, scrollOffset } = result.current;
+
+    expect(totalPages).toBe(3);
+    expect(scrollOffset).toEqual([0, 200, 400]);
+  });
+});

packages/nuka/src/hooks/use-measurement.tsx

@@ -27,7 +27,7 @@ export function useMeasurement({ element, scrollDistance }: MeasurementProps) {
 
     switch (scrollDistance) {
       case 'screen': {
-        const pageCount = Math.ceil(scrollWidth / visibleWidth);
+        const pageCount = Math.round(scrollWidth / visibleWidth);
 
         setTotalPages(pageCount);
         setScrollOffset(arraySeq(pageCount, visibleWidth));
@@ -56,7 +56,7 @@ export function useMeasurement({ element, scrollDistance }: MeasurementProps) {
       }
       default: {
         if (typeof scrollDistance === 'number') {
-          // find the number of pages required to scroll the all slides
+          // find the number of pages required to scroll all the slides
           // to the end of the container
           const pageCount = Math.ceil(remainder / scrollDistance) + 1;