JSX namespace is not defined in react 19+

[tshmieldev]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Affected package

main package

Steps to reproduce

Make a project in NextJS (using typescript, next15)
Use React-Markdown in a client component
Run build task

Actual behavior

I am using react-markdown in Next 15 (React 19)
Doing npm run build causes this problem

./node_modules/react-markdown/lib/complex-types.ts:25:21
Type error: Cannot find namespace 'JSX'.

  23 |
  24 | export type NormalComponents = {
> 25 |   [TagName in keyof JSX.IntrinsicElements]:
     |                     ^
  26 |     | keyof JSX.IntrinsicElements
  27 |     | C
``

After researching this topic, I found the fix: Import React and replace JSX with React.JSX

I would happily make a PR with this change if you allow it

Thanks
Wojtek

### Expected behavior

Not crash, allow the build to finish (that's what happens after my fix)

### Runtime

node@23

### Package manager

npm@10.8

### Operating system

macOS Sequoia 15

### Build and bundle tools

Next.js

[remcohaszing]

This issue is outdated. Update react-markdown.

[github-actions]

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