diff --git a/CHANGELOG.md b/CHANGELOG.md index a76c66692c006..973d088c258ed 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -1,3 +1,275 @@ +## 19.0.0 (December 5, 2024) + +Below is a list of all new features, APIs, deprecations, and breaking changes. Read [React 19 release post](https://react.dev/blog/2024/04/25/react-19) and [React 19 upgrade guide](https://react.dev/blog/2024/04/25/react-19-upgrade-guide) for more information. + +> Note: To help make the upgrade to React 19 easier, we’ve published a react@18.3 release that is identical to 18.2 but adds warnings for deprecated APIs and other changes that are needed for React 19. We recommend upgrading to React 18.3.1 first to help identify any issues before upgrading to React 19. + +### New Features + +#### React + +* Actions: `startTransition` can now accept async functions. Functions passed to `startTransition` are called “Actions”. A given Transition can include one or more Actions which update state in the background and update the UI with one commit. In addition to updating state, Actions can now perform side effects including async requests, and the Action will wait for the work to finish before finishing the Transition. This feature allows Transitions to include side effects like `fetch()` in the pending state, and provides support for error handling, and optimistic updates. +* `useActionState`: is a new hook to order Actions inside of a Transition with access to the state of the action, and the pending state. It accepts a reducer that can call Actions, and the initial state used for first render. It also accepts an optional string that is used if the action is passed to a form `action` prop to support progressive enhancement in forms. +* `useOptimistic`: is a new hook to update state while a Transition is in progress. It returns the state, and a set function that can be called inside a transition to “optimistically” update the state to expected final value immediately while the Transition completes in the background. When the transition finishes, the state is updated to the new value. +* `use`: is a new API that allows reading resources in render. In React 19, `use` accepts a promise or Context. If provided a promise, `use` will suspend until a value is resolved. `use` can only be used in render but can be called conditionally. +* `ref` as a prop: Refs can now be used as props, removing the need for `forwardRef`. +* **Suspense sibling pre-warming**: When a component suspends, React will immediately commit the fallback of the nearest Suspense boundary, without waiting for the entire sibling tree to render. After the fallback commits, React will schedule another render for the suspended siblings to “pre-warm” lazy requests. + +#### React DOM Client + +* `