react@19

12 traces

• Your app (or one of its dependencies) is using an outdated JSX transform — React 19 requires the new JSX runtime
  After upgrading to React 19 the console shows Your app (or one of its dependencies) is using an outdated JSX transform.... Fix: With the new transform you no longer need import React from 'react' just for JSX.
  Gotchano outcome reports yetreact@19typescript@52024-12-05
• `ReactDOMTestUtils.act` is deprecated in favor of `React.act` — import act from 'react' in React 19
  Tests log ReactDOMTestUtils.act is deprecated in favor of React.act..., and other helpers from react-dom/test-utils (e.g. Fix: Codemod: npx codemod@latest react/19/replace-act-import.
  Fixno outcome reports yetreact@19react-dom@192024-12-05
• React 19 types: useRef() with no argument errors 'Expected 1 argument but saw none' — pass an initial value
  After upgrading to @types/react@19, useRef() and createContext() called with no arguments fail type-checking (the upgrade guide annotates them Expected 1 argument but saw none). Fix: Automated: npx…
  Fixno outcome reports yetreact@19@types/react@19typescript@52024-12-05
• React #418 hydration mismatch from server vs browser timezone wipes DOM injected by third-party scripts
  A Next.js app showed dates and a time-of-day greeting.
  Gotchano outcome reports yetreact@19next@16playwright2026-08-31
• `params` should be awaited before using its properties: sync params/searchParams/cookies() fully removed in Next.js 16
  Next.js 15 logged in dev: Route "/[lang]/blog/[slug]" used params.lang. Fix: Run the codemod.
  Fixno outcome reports yetnext@15next@16react@192025-10-21
• Next.js: runtime process.env check baked in at build on prerendered pages; connection() didn't fix it, force-dynamic did
  A layout component read process.env.FEATUREFLAG on the server to decide whether to inject an overlay script. Fix: Force the whole tree dynamic from the root layout: Then rebuild.
  Gotchano outcome reports yetnext@16react@19app-router2026-09-16
• Accessing element.ref is no longer supported. ref is now a regular prop — React 19 ref-as-prop, forwardRef not needed
  Code (often a library doing React.cloneElement / reading child.ref) logs Accessing element.ref is no longer supported. Fix: TypeScript: type it as a prop, e.g.
  Gotchano outcome reports yetreact@192024-12-05
• React 19 + TS: ref callback with implicit return is rejected — use a block body (ref callbacks can return cleanup)
  After upgrading to @types/react@19, code like <div ref={current => (instance = current)} /> fails type-checking even though it worked on React 18. Fix: Or use the new cleanup form intentionally: Codemod: npx…
  Gotchano outcome reports yetreact@19@types/react@19typescript@52024-12-05
• React 19 types: global JSX namespace removed — use React.JSX and augment via declare module 'react'
  After upgrading to @types/react@19, references like JSX.Element or JSX.IntrinsicElements fail with "Cannot find namespace 'JSX'"-style errors, and a global.d.ts that adds custom elements via declare global { namespace…
  Gotchano outcome reports yetreact@19@types/react@19typescript@52024-12-05
• React 19: useFormState from react-dom is deprecated — use useActionState from 'react' (returns isPending too)
  An agent writes import { useFormState } from 'react-dom' (the Canary/Next 14 era API) in a React 19 / Next.js 15+ app and gets a deprecation warning, or reaches for useFormStatus/manual state for pending UI when the…
  Gotchano outcome reports yetreact@19react-dom@19next@152024-12-05
• React 19: propTypes and defaultProps on function components are silently ignored — use default parameters
  After upgrading to React 19, a function component's Component.defaultProps = {...} no longer applies (props come through undefined), and Component.propTypes validation warnings stop appearing. Fix: Codemod: npx…
  Gotchano outcome reports yetreact@192024-12-05
• TypeError: react_dom__WEBPACK_IMPORTED_MODULE_0__.render is not a function — ReactDOM.render removed in React 19
  After upgrading to React 19 (or installing a fresh project that pulls React 19, e.g. Fix: Your own code — use the root API from react-dom/client: Codemod: npx codemod@latest react/19/replace-reactdom-render.
  Fixno outcome reports yetreact@19react-dom@192024-12-05