feature: Migrate Angular 9 HN PWA to React 18 + TypeScript (pixel-perfect, visual-regression verified)#321
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…l regression parity - Port all components, services, models, styles, routing and PWA setup from Angular to React 18 + Vite - Replace RxJS services with React Context (SettingsContext) and async hooks (useHackerNewsApi) - Add Playwright visual regression suite (48 tests: every view x 3 themes x mobile/desktop + settings) passing at maxDiffPixelRatio 0.01 vs Angular baseline - Add Vitest unit tests for formatComment, SettingsContext, API functions and Item component - Remove Angular/RxJS/zone.js/karma/protractor toolchain; update README and CI Co-Authored-By: Lukas Burger <lukaskburger@gmail.com>
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Summary
Full rewrite of the Angular 9 Hacker News PWA to React 18 + TypeScript + Vite, with pixel-perfect parity enforced by a Playwright visual-regression suite. Every Angular component, service, model, style and the PWA service worker were ported 1:1; the Angular/RxJS/zone.js/karma/protractor toolchain was removed.
Parity is not asserted by eye — Angular baseline screenshots were captured first (Phase 0), then the React output is diffed against them. 48/48 visual-regression tests pass within
maxDiffPixelRatio: 0.01(7 scenarios × 3 themes × 2 viewports + settings panel).Architecture mapping
HackerNewsAPIService(RxJSObservable+unfetch)src/hooks/useHackerNewsApi.ts— asyncfetchfunctions + genericuseApiFetch<T>hookSettingsServicesrc/contexts/SettingsContext.tsx—SettingsProvider/useSettings(), samelocalStoragekeys +prefers-color-schemelistenerCommentPipesrc/utils/formatComment.ts*.component.ts/html/scss.scssapp.routes.ts(lazy modules)src/routes.tsxwithReact.lazyfor item/user pagesngsw-config.json)vite-plugin-pwa/ Workbox (NetworkFirstfor the HN API)Notable porting detail (non-obvious)
Angular's
ViewEncapsulationimplicitly scopes component CSS. Flattening to global SCSS leaked rules across components and broke parity until fixed, e.g.:header h1 { font-size: 16px }shrank the Settings popup title → render<Settings>outside<header>..item-details-view p { margin: 2px 0 }collapsed comment paragraph spacing → scoped to.laptop > p, .mobile > pso it doesn't reachdangerouslySetInnerHTMLcomment bodies.Theme structural selectors (
.wrapper,#header,.popup,.loader, …) are kept as literal global class names (not CSS modules) so the_themes.scssmixin selectors keep matching.Testing
npm test— Vitest unit tests (17):formatComment,SettingsContext(persistence/theme/toggles),useHackerNewsApi(mocked fetch incl. poll sub-fetch tallying),Itemrendering. All pass.npm run test:vr— Playwright visual regression. 48/48 pass.npm run lint,npm run typecheck,npm run build— all clean.Screenshots
Link to Devin session: https://app.devin.ai/sessions/80307157bda94caa8de20724c3b44f4d
Requested by: @lburgers
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