React
Baseline: React 19.2 with React Compiler 1.0 assumed. See Stack baseline — 2026-2027.
The compiler changes advice, not just versions. Auto-memoization means most manual
useMemo/useCallbackguidance is now wrong for new code. Files below still carrying the old advice are flagged; the rewrite is phase 7 in Modernization plan — 2026-2027 interview prep.
Mental model
| File | Covers |
|---|---|
| React: the component model | what React is, JSX, the component model |
| React Elements vs Components | elements are descriptions, components are functions |
| React State vs Props | the two inputs, and who owns each |
| Prop Children | composition via children |
| React Fragment | grouping without a wrapper node |
| Key Property in React | list identity, and why index keys corrupt state |
Rendering internals
| File | Covers |
|---|---|
| Virtual DOM in React | what the VDOM is and isn’t |
| Shadow DOM vs Virtual DOM | unrelated concepts with confusable names |
| React Fiber | the fiber architecture |
| React Reconciliation | diffing, bailouts, when subtrees remount |
| Concurrent Rendering — useTransition, useDeferredValue, How Priorities Work | interruptible rendering, transitions |
| React Lifecycle | mount/update/unmount, effects as the modern equivalent |
| Synthetic Events in React | the event delegation layer |
| React Portal | rendering outside the parent DOM node |
Hooks
| File | Covers |
|---|---|
| The hooks, and which note goes deep on each | the built-in set |
| useEffect Deep — Cleanup, StrictMode Double-Invoke, Dep-Array Bugs, Effect Events | dependencies, cleanup, and when you don’t need an effect |
| useRef Hook in React | mutable boxes and DOM handles |
| Stale Closures and the Rules of Hooks | the classic hook bug and the rules that prevent it |
| Controlled vs uncontrolled components | form state ownership |
Performance
| File | Covers |
|---|---|
| React Compiler | the compiler — read this before the memo files |
| React.memo | manual memoization: mechanism, and when the compiler bails out |
| React Pure Components | purity and bailout conditions |
| Context Performance Traps | why context re-renders everything, and the splitting fix |
Server rendering and data
| File | Covers |
|---|---|
| React Server Components | RSC — what runs where |
| Hydration — Selective, Progressive, Mismatches | attaching to server HTML, and mismatch errors |
| Suspense for Data — vs Suspense for Code, Error Boundaries, Streaming SSR | Suspense as a data-loading boundary |
| React 19 — Actions, useActionState, useOptimistic, use(), ref as Prop | what landed in 19 |
Patterns
| File | Covers |
|---|---|
| Higher-Order Components (HOC) | higher-order components (largely superseded by hooks) |
| MVC, and what React actually is | how React relates to MVC |
Known gaps
- React Router — no dedicated note. Covered incidentally in Project Structure — Senior Interview Prep and Rendering Modes — Senior Interview Prep.
- Server Actions / forms (
useActionState,useFormStatus) — thin.
A 9,850-line vendored copy of a third-party interview-questions repo previously sat at this path. It carried sponsor banners, was largely class-component-era React, and duplicated the files above. It was removed in phase 2; recover it from git history if needed.