[React 19] - `ReactElement` created from `React.createElement` are not renderable anymore about react

[eps1lon]

You probably have different versions of React installed. Or a 3rd party library is bundling the JSX runtime of a different React version.

The repro is too big for us to check out. Can you trim it down to something minimal?

[SukkaW]

You probably have different versions of React installed

I don't know. Since it is using Next.js Pages Router, Next.js would most likely not use its bundled version of React.

Or a 3rd party library is bundling the JSX runtime of a different React version.

No, we do not use any CSS-in-JS that requires non-React jsx runtime. It uses style9, a similar AoT CSS-in-JS approach to Facebook's stylex.

The repro is too big for us to check out. Can you trim it down to something minimal?

Lemme give it a shot!

[SukkaW]

Update

I know what happened and it is not an issue of React.

So the serialization assumes the $$typeof would most likely be Symbol.for('react.element'), which is true in 2018 (when Dan implements that serialization process for the https://react.dev).

Years later, the coming React 19 is introducing new shapes of react element (#28813), and therefore objects with Symbol.for('react.transitional.element') are produced. The serialization process doesn't handle Symbol.for('react.transitional.element'), hence the crash.

Also, because the original $$typeof information is lost during the serialization process, the error A React Element from an older version of React was rendered was never reported.