Align logic more closely with the original nprogress, add React boundary tests

.github/copilot-instructions.md

@@ -7,7 +7,7 @@ changes agent behaviour and cannot be inferred from the codebase or tooling.
 
 TypeScript React library providing a slim progress bar primitive via three
 patterns: `useNProgress` hook, `NProgress` render-props component, and
-`withNProgress` HOC. Exports logic only — no rendering. All exports go through
+`withNProgress` HOC. Exports logic only, not rendering. All exports go through
 `src/index.tsx`. Types live in `src/types.ts`.
 
 ## Key Commands
@@ -22,14 +22,15 @@ npm run format    # fix lint and formatting
 
 ### Comments
 
-- Use `//` line comments only — never `/* */` or `/** */`
+- Use `//` line comments only, never `/* */` or `/** */`
 - Explain _why_, not _what_; wrap at 80 characters
+- End every comment with a full stop, even single-line comments
 
 ### Language
 
 Use **New Zealand English** in all user-facing text, variable names, and
 comments (e.g. "colour", "behaviour", "organisation"). Standardised API names
-(`color`, `textAlign`) are fixed — leave them unchanged.
+(`color`, `textAlign`) are fixed: leave them unchanged.
 
 ```javascript
 const progressColour = '#0066cc'
@@ -49,16 +50,42 @@ subject, no trailing period, blank line between subject and body.
 
 Managed by Renovate (`config:js-lib` preset):
 
-- `devDependencies` — pinned exact versions (no `^` or `~`)
-- `dependencies` — caret ranges (`^`)
-- `peerDependencies` — explicit OR ranges (e.g. `^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0`)
+- `devDependencies`: pinned exact versions (no `^` or `~`)
+- `dependencies`: caret ranges (`^`)
+- `peerDependencies`: explicit OR ranges (e.g. `^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0`)
 - Do **not** add `allowedVersions` to `renovate.json` without a documented reason
 
 ## Testing
 
 - **100% code coverage** required across all build formats
 - Always run `npm test` after changes; use `npm run test:src` for quick
   source-only feedback during development
+- Use `npm run test:react` for the full React version matrix independently.
+  It also runs as part of `npm test` (via the `test:*` glob).
+
+### React version matrix
+
+We test boundary versions only: first and last minor of each supported
+major. See `test/react/` for current versions.
+
+Current boundaries: 16.14, 17.0, 18.0, 18.3, 19.0.
+
+React 16.14 is the practical lower bound. Hooks require 16.8 and
+`@testing-library/react-hooks` requires 16.9.
+
+When adding a new boundary:
+
+1. Add `test/react/<version>/package.json` with correct `react`,
+   `react-dom`, and `@testing-library/react` (12.x for React 16–17,
+   16.x for React 18+). React 16–17 also need
+   `@testing-library/react-hooks` (8.x) and `react-test-renderer`.
+2. Replace the previous "latest minor" for that major.
+3. Verify with a single-version run before the full matrix:
+   ```bash
+   cd test/react/<version> && npm i --no-package-lock --quiet --no-progress
+   REACT_VERSION=<version> npx jest --config ./scripts/jest/config.src.js --coverage false
+   ```
+4. Update the boundary list above.
 
 ## Examples
 
@@ -85,7 +112,23 @@ needed but test on CodeSandbox before merging.
 Do not bump vite, @vitejs/plugin-react, next, or typescript in examples
 beyond the versions in the reference templates.
 
+## Writing Style
+
+- Avoid marketing or promotional language. State facts plainly.
+- Follow best practices for technical writing: be clear, direct, and
+  concise.
+- Avoid em dashes. Use colons, commas, or separate sentences instead.
+- Use present tense and active voice where practical.
+- Keep sentences short. One idea per sentence.
+
 ## Versioning
 
-Strict semver — no breaking changes without a major version bump, including
+Strict semver: no breaking changes without a major version bump, including
 technical refactors.
+
+## Documentation
+
+- After each code change, update all related docs and markdown files
+  (README.md, MIGRATION.md, example READMEs, etc.) in the same pass.
+- Do not manually modify CHANGELOG.md. It is auto-generated during
+  release.

MIGRATION.md

@@ -1,5 +1,35 @@
 # Migrating
 
+## v6.0.0
+
+Trickle pacing was adjusted to more closely match the original
+[nprogress](https://github.com/rstacruz/nprogress) behaviour.
+
+### `incrementDuration` default changed from `800` to `200`
+
+The previous default of `800` meant each trickle took roughly one second
+(animation wait plus increment delay). The new default of `200` matches
+the original library's `trickleSpeed` and results in faster trickle
+pacing.
+
+**Action required:** if you were relying on the old default pacing,
+explicitly pass `incrementDuration={800}` to restore the previous
+behaviour.
+
+### Intermediate progress updates no longer wait for `animationDuration`
+
+Non-completion `set()` calls previously waited `animationDuration`
+(200 ms) before advancing the internal queue. This wait has been
+removed for intermediate updates so that only `incrementDuration`
+controls trickle pacing. The completion path (`set(1)`) still waits
+`animationDuration` before marking the bar as finished, giving
+consumers time to animate the bar to 100% before it disappears.
+
+**Action required:** none in most cases. If your rendering code relied
+on intermediate progress updates being spaced at least
+`animationDuration` apart, you may need to adjust your
+transition/animation timing.
+
 ## v5.0.0
 
 The prop-types package is no longer required for using the UMD builds.

README.md

@@ -111,7 +111,7 @@ render(<Enhanced isAnimating />, document.getElementById('root'))
 **Props**
 
 - `animationDuration` - _Optional_ Number indicating the animation duration in `ms`. Defaults to `200`.
-- `incrementDuration` - _Optional_ Number indicating the length of time between progress bar increments in `ms`. Defaults to `800`.
+- `incrementDuration` - _Optional_ Number indicating the length of time between progress bar increments in `ms`. Defaults to `200`.
 - `isAnimating` - _Optional_ Boolean indicating if the progress bar is animating. Defaults to `false`.
 - `minimum` - _Optional_ Number between `0` and `1` indicating the minimum value of the progress bar. Defaults to `0.08`.
 

package.json

@@ -20,6 +20,7 @@
     "clean:compiled": "shx rm -rf compiled",
     "clean:coverage": "shx rm -rf coverage",
     "clean:dist": "shx rm -rf dist",
+    "clean:react": "node ./scripts/clean-react.js",
     "compile": "tsc -p tsconfig.base.json",
     "format": "npm run lint -- --fix && prettier --write \"**/*.{js,ts,tsx}\"",
     "lint": "eslint .",
@@ -30,6 +31,7 @@
     "test:cjs": "jest --config ./scripts/jest/config.cjs.js",
     "test:cjsprod": "jest --config ./scripts/jest/config.cjsprod.js",
     "test:es": "jest --config ./scripts/jest/config.es.js",
+    "test:react": "node ./scripts/test-react.js",
     "test:src": "jest --config ./scripts/jest/config.src.js",
     "test:umd": "jest --config ./scripts/jest/config.umd.js",
     "test:umdprod": "jest --config ./scripts/jest/config.umdprod.js",

scripts/clean-react.js

@@ -0,0 +1,25 @@
+// Cleans node_modules from each test/react/<version> directory while preserving
+// the package.json file.
+const fs = require('fs')
+const os = require('os')
+const path = require('path')
+
+const reactDir = path.join(process.cwd(), 'test', 'react')
+
+fs.readdirSync(reactDir, { withFileTypes: true })
+  .filter((entry) => entry.isDirectory())
+  .forEach((entry) => {
+    const dir = path.join(reactDir, entry.name)
+    const pkgJsonPath = path.join(dir, 'package.json')
+
+    if (!fs.existsSync(pkgJsonPath)) {
+      return
+    }
+
+    // Preserve package.json by copying to a temporary location.
+    const tmpPath = path.join(os.tmpdir(), `${entry.name}-package.json`)
+    fs.copyFileSync(pkgJsonPath, tmpPath)
+    fs.rmSync(dir, { force: true, recursive: true })
+    fs.mkdirSync(dir, { recursive: true })
+    fs.copyFileSync(tmpPath, pkgJsonPath)
+  })

scripts/jest/config.src.js

@@ -1,10 +1,74 @@
+const path = require('path')
+
+// When REACT_VERSION is set (e.g. "18.0"), resolve react, react-dom and
+// @testing-library/react from the matching test/react/<version> directory so
+// the test suite runs against that specific React version.
+const generateReactVersionMappings = (reactVersion) => {
+  if (!reactVersion) {
+    return {}
+  }
+
+  const testDir = path.join(process.cwd(), 'test', 'react', reactVersion)
+  const [major] = reactVersion.split('.').map(Number)
+
+  const reactDir = path.dirname(
+    require.resolve('react/package.json', { paths: [testDir] }),
+  )
+  const reactDomDir = path.dirname(
+    require.resolve('react-dom/package.json', { paths: [testDir] }),
+  )
+
+  const mappings = {
+    '^react$': require.resolve('react', { paths: [testDir] }),
+    '^react-dom$': require.resolve('react-dom', { paths: [testDir] }),
+    '^react-dom/(.*)$': `${reactDomDir}/$1`,
+    '^react/(.*)$': `${reactDir}/$1`,
+  }
+
+  // React 16 and 17 use @testing-library/react 12.x which does not export
+  // renderHook. A shim re-exports it from @testing-library/react-hooks instead.
+  if (major < 18) {
+    mappings['^@testing-library/react$'] = path.join(
+      testDir,
+      '..',
+      'testing-library-shim.js',
+    )
+  } else {
+    mappings['^@testing-library/react$'] = require.resolve(
+      '@testing-library/react',
+      { paths: [testDir] },
+    )
+  }
+
+  return mappings
+}
+
+// React 16 and 17 boundary tests produce harmless "wrong act()" warnings from
+// @testing-library/react-hooks. A setup file suppresses them.
+const generateSetupFiles = (reactVersion) => {
+  if (!reactVersion) {
+    return []
+  }
+
+  const [major] = reactVersion.split('.').map(Number)
+  if (major < 18) {
+    return [path.join(__dirname, 'setupReact.js')]
+  }
+
+  return []
+}
+
 module.exports = {
   collectCoverage: true,
   collectCoverageFrom: ['src/*.{ts,tsx}'],
   moduleFileExtensions: ['ts', 'tsx', 'js'],
+  moduleNameMapper: {
+    ...generateReactVersionMappings(process.env.REACT_VERSION),
+  },
   preset: 'ts-jest',
   rootDir: process.cwd(),
   roots: ['<rootDir>/test'],
+  setupFilesAfterEnv: generateSetupFiles(process.env.REACT_VERSION),
   testEnvironment: 'jsdom',
   testMatch: ['<rootDir>/test/*.spec.ts?(x)'],
   transform: { '^.+\\.(js|tsx?)$': 'ts-jest' },

scripts/jest/setupReact.js

@@ -0,0 +1,15 @@
+// Suppresses the "wrong act()" console.error warnings that
+// @testing-library/react-hooks emits on React 16 and 17. The package uses
+// react-test-renderer internally while state updates flow through react-dom,
+// triggering a harmless mismatch warning.
+const originalError = console.error
+
+console.error = (...args) => {
+  if (
+    typeof args[0] === 'string' &&
+    args[0].includes("It looks like you're using the wrong act()")
+  ) {
+    return
+  }
+  originalError.call(console, ...args)
+}

scripts/test-react.js

@@ -0,0 +1,39 @@
+// Installs dependencies and runs the src test suite against each React version
+// defined in test/react/<version>.
+const { execSync } = require('child_process')
+const fs = require('fs')
+const path = require('path')
+
+const reactDir = path.join(process.cwd(), 'test', 'react')
+
+const versions = fs
+  .readdirSync(reactDir, { withFileTypes: true })
+  .filter((entry) => entry.isDirectory())
+  .filter((entry) =>
+    fs.existsSync(path.join(reactDir, entry.name, 'package.json')),
+  )
+  .map((entry) => entry.name)
+  .sort()
+
+for (const version of versions) {
+  const dir = path.join(reactDir, version)
+
+  console.log(`Starting React ${version} tests`)
+
+  execSync('npm i --no-package-lock --quiet --no-progress', {
+    cwd: dir,
+    stdio: 'inherit',
+  })
+
+  try {
+    execSync(
+      `REACT_VERSION=${version} npx jest --config ./scripts/jest/config.src.js --coverage false`,
+      { stdio: 'inherit' },
+    )
+  } catch {
+    console.error(`Fail testing React ${version}`)
+    process.exit(1)
+  }
+
+  console.log(`Success testing React ${version}`)
+}

src/createTimeout.ts

@@ -1,13 +1,18 @@
+// Uses requestAnimationFrame rather than setTimeout for smoother animation
+// timing. Note that rAF is throttled or paused in background tabs, so progress
+// will stall when the tab is hidden and resume when it regains focus.
 export const createTimeout = () => {
   let handle: number | undefined
 
   const cancel = (): void => {
-    if (handle) {
+    if (handle !== undefined) {
       window.cancelAnimationFrame(handle)
     }
   }
 
   const schedule = (callback: () => void, delay: number): void => {
+    cancel()
+
     let deltaTime
     let start: number | undefined
     const frame: FrameRequestCallback = (time) => {