React Fix, Crash & Optimization Guide

React is a JavaScript library for building user interfaces from components, maintained by Meta and a large open-source community. It powers everything from single-page apps to the view layer inside frameworks like Next.js and Remix.

Install / First Setup

The current recommended starting point is Vite:

npm create vite@latest my-app -- --template react
cd my-app
npm install
npm run dev

Add React to an existing project with npm install react react-dom. Note: create-react-app is deprecated and no longer recommended for new projects — use Vite or a meta-framework (Next.js, Remix) instead.

Common Issues & Fixes

"Too many re-renders. React limits the number of renders"

Cause: A setState call runs unconditionally during render, creating an infinite update loop. Fix: Move the update into useEffect, or guard it behind an event handler / condition so it does not fire on every render.

"Cannot update a component while rendering a different component"

Cause: Calling another component's setter directly during render instead of through props or effects. Fix: Lift state up or update the child via props; schedule cross-component updates in useEffect.

npm install fails with peer dependency conflict

Cause: Two packages require incompatible versions of React or a shared dependency. Fix: Prefer resolving versions, but as a short-term fix npm install --legacy-peer-deps bypasses the strict check. Avoid making this permanent.

Component not re-rendering after state change

Cause: Mutating state in place (e.g. state.push(...)) so React's reference check sees no change. Fix: Return a new object/array: setItems([...items, next]). For objects use the spread operator.

Breaking changes after React 18 → 19 upgrade

Cause: Removed APIs or changed behavior (e.g. ref handling, stricter hydration). Fix: Read the upgrade guide, update @types/react/@types/react-dom, and replace deprecated patterns like string refs or ReactDOM.render with createRoot.

Performance & Optimization

• Low-End (4–8 GB RAM): Keep the dev dependency tree small; run one dev server at a time. Disable browser extensions that thrash the DOM. Vite's dev server is lightweight and fast.
• Mid (16 GB): Use React.memo on expensive children, useMemo/useCallback for stable references, and split routes with React.lazy + Suspense. Build with npm run build for production minification.
• Workstation (32 GB+): Run multiple project watchers, profile with the React DevTools "Profiler" and the why-did-you-render helper during investigation. Use concurrent features (useTransition, startTransition) to keep the UI responsive.

General wins: avoid inline object/function props on memoized children, throttle expensive computations, and code-split heavy libraries (charts, editors) with dynamic imports.

Version & Compatibility Notes

• React 18 introduced concurrent rendering, automatic batching, and useTransition/useDeferredValue.
• React 19 adds Actions, the use hook, and native form/<Context> improvements; it is the current major.
• React itself has no required runtime beyond a modern browser and a bundler; Node is needed only for the dev toolchain (Node 18+ recommended). For exact per-release details, consult official release notes.

FAQ

Q: What is the difference between React 18 and React 19? A: React 19 builds on React 18's concurrency with first-class Actions, the use hook, and improved hydration/error handling. Most apps upgrade with minor changes.

Q: Why is create-react-app no longer recommended? A: It is officially deprecated and unmaintained. Vite (or a meta-framework) provides faster dev startup and modern defaults.

Q: How do I stop unnecessary re-renders? A: Memoize children with React.memo, stabilize callbacks with useCallback, and avoid passing new object/array literals as props on every render.

Q: How do I lazy-load a component? A: Use const Comp = React.lazy(() => import('./Comp')) wrapped in <Suspense fallback={...}>. This splits it into a separate bundle.

Q: Why doesn't my state update show immediately? A: State updates are asynchronous and batched. Read the updated value inside useEffect or after the next render rather than right after the setter call.

Q: Do I need TypeScript for React? A: No, but @types/react and @types/react-dom are recommended for type safety; many teams adopt TypeScript for larger codebases.

Related Guides

• Next.js Fix & Optimization Guide
• Vue Fix & Optimization Guide
• Dev RAM Calculator

Accuracy Note

Commands and paths reflect common, real-world setups as of 2026-08. Always verify against your installed version and OS. When in doubt, consult the official React documentation.