Switch from JSX.Element to React.JSX.Element

[ebroder]

Description

The global JSX namespace has been deprecated for around two and a half years now in favor of using React.JSX, and as of the type declarations for React 19, it's been fully removed. By switching to the new namespace, this package maintains compatibility with React 19.

Without this change, attempting to use React 19 with slate-react and TypeScript results in typechecking errors:

node_modules/slate-react/dist/components/text.d.ts:8:59 - error TS2503: Cannot find namespace 'JSX'.

8     renderPlaceholder: (props: RenderPlaceholderProps) => JSX.Element;
                                                            ~~~

node_modules/slate-react/dist/components/text.d.ts:9:47 - error TS2503: Cannot find namespace 'JSX'.

9     renderLeaf?: ((props: RenderLeafProps) => JSX.Element) | undefined;
                                                ~~~

node_modules/slate-react/dist/components/text.d.ts:10:47 - error TS2503: Cannot find namespace 'JSX'.

10     renderText?: ((props: RenderTextProps) => JSX.Element) | undefined;
                                                 ~~~

Issue

N/A

Example

Context

The React.JSX namespace was introduced and global JSX was deprecated both in DefinitelyTyped/DefinitelyTyped#64464, which was published as v18.2.6 of @types/react (n.b.: version numbers in @types/ packages are only loosely connected to upstream version numbers).

Since TypeScript is structurally-typed, the types React.JSX.Element and JSX.Element should be functionally equivalent to the typechecker, so as long as users have a version of @types/react that includes both declarations, this should not cause a backwards compatibility issue.

Ideally, we would enforce that users had v18.2.6 or later of @types/react, but given the nature of type dependencies, that's not possible. (There's no way to have a non-dev dependency introduce new dev dependencies). But presumably anyone who is proactively updating this package is also updating their type declarations as well.

Checks

• The new code matches the existing patterns and styles.
• The tests pass with yarn test.
• The linter passes with yarn lint. (Fix errors with yarn fix.)
• The relevant examples still work. (Run examples with yarn start.)
• You've added a changeset if changing functionality. (Add one with yarn changeset add.)

[changeset-bot]

🦋 Changeset detected

Latest commit: 54b4063

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
slate-react	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

[dylans]

I'm ok with this for now, but I'd actually like to see us move away from using import React from 'react' and more directly import what we use, but that's a much bigger change.

[ebroder]

Is there anything I can do on my end to encourage merging and releasing this? AFAIK it's the last blocker for us to upgrade.