React 19 required

3.14 upgrades the monorepo to React 19.2.7.

If you deploy the shipped OHIF viewer as-is, this is invisible — the app bundles its own React. It matters in two cases: you consume OHIF's published packages from npm, or you maintain a third-party extension or mode.

@ohif/ui-next now declares React as a peer dependency

Before (3.13):

"dependencies": {
  "react": "18.3.1",
  "react-dom": "18.3.1"
}

After (3.14):

"peerDependencies": {
  "react": "^19.2.7",
  "react-dom": "^19.2.7"
}

With OHIF 3.14, your application must supply React itself, because @ohif/ui-next no longer installs a copy of its own. A peer dependency states a requirement on your project — it does not deliver the package to you.

This is what keeps a single React instance on the page. Two copies of React have separate internal state: hooks throw Invalid hook call, and context created by one copy is invisible to components rendered by the other.

What to do: upgrade your application to React 19.2.7 or newer. Any 19.x at or above that version satisfies the range.

Extensions and modes require React 19

Every OHIF extension and mode declares react and react-dom 19.2.7 as peer dependencies. A third-party extension built against React 18 must be upgraded before it will work with 3.14.

UMD builds require a React 19 host at runtime

OHIF's UMD artifacts that externalize React (notably @ohif/ui-next) are compiled with the React Compiler, and the compiled output reads useMemoCache off the host's React. That API exists only in React 19.

This failure surfaces at runtime, not install time — a React 18 host loads the bundle and breaks when a compiled component first renders, with no package-manager warning beforehand. If you load OHIF UMD bundles against a global React, confirm that global is React 19 before upgrading.

React 19 removals that affect extension code

React 19 removed a number of long-deprecated APIs. The ones most likely to appear in extension or mode code:

Removed in React 19	Use instead
ReactDOM.render, ReactDOM.hydrate	createRoot, hydrateRoot
ReactDOM.unmountComponentAtNode	root.unmount()
findDOMNode	refs
runtime propTypes (silently ignored)	TypeScript types
defaultProps on function components	default parameter values
string refs, legacy context	callback or object refs, createContext

forwardRef is not removed, but it is no longer necessary: React 19 function components accept ref as an ordinary prop. OHIF's own components were converted, and extension code can be converted at your convenience.

See React's version 19 upgrade guide for the complete list.

TypeScript types

OHIF moves to @types/react 19.2.17 and @types/react-dom 19.2.3. If you maintain TypeScript extension code, types-react-codemod's preset-19 handles the mechanical changes — chiefly that useRef() now requires an argument, and ReactElement generic defaults changed:

npx types-react-codemod@latest preset-19 ./src

The React Compiler, and what it means for your extension

3.14 enables the React Compiler across OHIF's own source. What that means for you depends on how you build.

You consume OHIF from npm and build your extension yourself. The compiler applies to OHIF's code, not yours, and nothing is required. If you want the same automatic memoization, enable babel-plugin-react-compiler in your own build.

You fork the repository and add your extension under extensions/ or modes/. Your code becomes part of OHIF's build and CI, so the same tooling that covers OHIF's own components covers yours:

1. It is compiled. The compiler's scope is every src/ directory under platform/, extensions/ and modes/. Most components are fine. A component that reads or mutates state outside React during render — a cornerstone3D viewport or overlay is the typical case — can be memoized in a way that stops it updating; the opt-outs below are for that.
2. The React 19 lint rules apply. pnpm lint:compiler flags forwardRef and prop-types, which React 19 no longer needs.
3. The coverage gate includes it. pnpm run compiler:coverage:ci reports any function the compiler declines to memoize. Fix it, or record it in .react-compiler-budget.json.
4. The lint budget includes it. pnpm run lint:compiler:ci compares the react-hooks/* error and warning counts against .react-compiler-lint-budget.json. Adjust the budget when your code moves them.

Both gates fail CI until their budget file matches, and both print exactly which file and which entry is involved, so the fix is never a guess.

Opting a file out

Put 'use no memo'; as the first statement in the file, with a comment above it saying what broke, and add the file's path to fileOptOuts in .react-compiler-budget.json. The compiler skips the whole file, and the gate checks that the entry exists. Prefer this when one or two components are the problem.

Opting a directory out

Add it to excluded in react-compiler.scope.cjs at the repository root:

const excluded = [
  'platform/ui',
  'extensions/my-extension',
];

That one list drives the compiler in both build pipelines, the compiler lint rules and the coverage gate, so they cannot disagree. The gate names every directory it skips:

excluded by react-compiler.scope.cjs: 12 file(s) under extensions/my-extension

An excluded directory is outside the compiler's world entirely — not compiled, not linted by the compiler rules, not gated — the way platform/ui is.