# What changed in react

> 51 changes in react 19 from its official release notes, upgrade guides and advisories: 2 breaking, 1 deprecations, 7 security, 12 new APIs and options. Each one cited. Sources checked 2026-10-17. HTML: https://unstale.sh/npm/react/

To see which of these apply to a repository, run `npx @unstale/cli init` in it.

## react 19

### Breaking changes

- Moves react-server-dom-webpack/*.unbundled to the private react-server-dom-unbundled package. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Types were hardened in React Server Components, which may affect developer-written type usage. (19.2.6) — [release notes](https://github.com/react/react/releases/tag/v19.2.6)

### Security

- Adds nonce to rendered import maps. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Added more DoS mitigations to Server Actions to improve application security. (19.2.4) — [release notes](https://github.com/react/react/releases/tag/v19.2.4)
- Hardened Server Components to improve application security. (19.2.4) — [release notes](https://github.com/react/react/releases/tag/v19.2.4)
- Added more DoS mitigations to Server Actions. (19.1.5) — [release notes](https://github.com/react/react/releases/tag/v19.1.5)
- Hardened Server Components against security threats. (19.1.5) — [release notes](https://github.com/react/react/releases/tag/v19.1.5)
- Added more DoS mitigations to Server Actions. (19.0.4) — [release notes](https://github.com/react/react/releases/tag/v19.0.4)
- Server Components were hardened against security threats. (19.0.4) — [release notes](https://github.com/react/react/releases/tag/v19.0.4)

### Deprecations

- Development builds warn when a component appears to have been unblocked by calling use() conditionally. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)

### New APIs and options

- Adds an API for assigning transition types to React View Transition animations. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Adds a react-dom API that marks a Suspense subtree as browser-only when used with use(). (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Adds fetchPriority support for module resources. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Adds refs to Fragment components to support composable platform behavior. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Adds support for the maskType SVG prop. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Adds support for the onFullscreenChange event. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Adds support for the onFullscreenError event. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Allows overriding request.timeOrigin through options.startTime. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Adds an option to observe when a subtree defers rendering to the browser. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Enables React integration with the Trusted Types API. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Adds an option to allow partial streams in the Flight Client. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Adds the ViewTransition component to power View Transition animations in React. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)

### Performance

- Improves the transport protocol used by React Server Components. (19.1.10, 19.2.9, 19.3.1) — [release notes](https://github.com/react/react/releases/tag/v19.3.1), [release notes](https://github.com/react/react/releases/tag/v19.2.9), [release notes](https://github.com/react/react/releases/tag/v19.1.10)
- Avoids setting innerHTML when its value has not changed. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Batches updates from resize events until the next frame. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Performance improvements when decoding React Server Components. (19.0.8, 19.1.9, 19.2.8) — [release notes](https://github.com/react/react/releases/tag/v19.2.8), [release notes](https://github.com/react/react/releases/tag/v19.1.9), [release notes](https://github.com/react/react/releases/tag/v19.0.8)
- React Server Components received performance improvements that may improve application runtime behavior. (19.2.6) — [release notes](https://github.com/react/react/releases/tag/v19.2.6)
- React Server Components received performance improvements that may improve application runtime behavior. (19.1.7) — [release notes](https://github.com/react/react/releases/tag/v19.1.7)
- Performance improvements make React Server Components more efficient. (19.0.6) — [release notes](https://github.com/react/react/releases/tag/v19.0.6)

### Behavior and default changes

- Adds support for transporting Error.cause through Flight replies. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Allows Server Components to render context providers from client modules. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Includes submitter in submit events and uses the FormData submitter parameter. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Transitions render independently, so a slow transition no longer holds up unrelated transitions. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Transitions render independently instead of being entangled into one render. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)

### Tooling

- Types were hardened for React Server Components, improving type safety for developers using them. (19.1.7) — [release notes](https://github.com/react/react/releases/tag/v19.1.7)
- Type hardening improves the type surface for React Server Components. (19.0.6) — [release notes](https://github.com/react/react/releases/tag/v19.0.6)

### Fixes and other changes

- Adds support for transporting AggregateError.errors through Flight replies. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Recognizes credentialless as a boolean iframe attribute and suggests its correct casing. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Updates defaultValue handling for number inputs to match other input types. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Fires onReset when forms are automatically reset. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Forwards the nonce option when preloading modules. (19.3.0) — [release notes](https://github.com/react/react/releases/tag/v19.3.0)
- Fixed missing FormData entries in Server Actions. (19.0.7, 19.1.8, 19.2.7) — [release notes](https://github.com/react/react/releases/tag/v19.2.7), [release notes](https://github.com/react/react/releases/tag/v19.1.8), [release notes](https://github.com/react/react/releases/tag/v19.0.7)
- React Server Components add more cycle protections. (19.2.5) — [release notes](https://github.com/react/react/releases/tag/v19.2.5)
- Adds extra loop protection to React Server Functions. (19.2.3) — [release notes](https://github.com/react/react/releases/tag/v19.2.3)
- Promise cycles and toString behavior on Server Functions were patched. (19.0.2, 19.1.3, 19.2.2) — [release notes](https://github.com/react/react/releases/tag/v19.2.2), [release notes](https://github.com/react/react/releases/tag/v19.1.3), [release notes](https://github.com/react/react/releases/tag/v19.0.2)
- React Server Component fixes were brought to Server Actions. (19.2.1) — [release notes](https://github.com/react/react/releases/tag/v19.2.1)
- Adds extra loop protection to React Server Functions, helping prevent excessive or infinite execution loops. (19.1.4) — [release notes](https://github.com/react/react/releases/tag/v19.1.4)
- React Server Component fixes are now included in Server Actions. (19.1.2) — [release notes](https://github.com/react/react/releases/tag/v19.1.2)
- React Server Components add more cycle protections. (19.0.5) — [release notes](https://github.com/react/react/releases/tag/v19.0.5)
- React Server Functions add extra loop protection to prevent problematic execution loops. (19.0.3) — [release notes](https://github.com/react/react/releases/tag/v19.0.3)
- React Server Component fixes were brought to Server Actions. (19.0.1) — [release notes](https://github.com/react/react/releases/tag/v19.0.1)