[React 19] react-is isFragment doesn't worked

[JulCyan]

Project use react version is 17.0.2 and not fixed version for react-is
To fix bug: now I fixed the react-is version to 17.0.2 in package.json , or else it will autoupgrade to the latest version 19.0.0

react-is version 19.0.0

Steps To Reproduce

import { isFragment } from "react-is";  

const fragment = <></>;
console.log("isFragment", isFragment(fragment));

The current behavior

// isFragment false

The expected behavior

// isFragment true

[eps1lon]

Thank you for reporting.

This seems to work in a minimal example: https://codesandbox.io/p/sandbox/magical-rosalind-qkf43m?workspaceId=ws_NXrhLjqHgWvFjhiKcfVFu6

Your version of react-is is probably not matching the version of React you're using. react-is must always match the version of react. Otherwise it may not work correctly.

[JulCyan]

@eps1lon
Sorry, I just seen, wish not too late, this is an example: https://codesandbox.io/p/sandbox/react-19-isfragment-forked-plwtlh
react-is version is >=17.0.2, like in my son project package, it can be use is react18 project and react17 project as dep
and anohter example, react-is version is <19.0.0 :https://codesandbox.io/p/sandbox/react-19-isfragment-forked-fytjp8
Before 19.0.0 released, it's all working, but now the first example is false, of course I can fixed react-is version in my project, but I think it's not necessary
up to you, If this's not a bug, close it, and thanks for your help

[Mathias-S]

@JulCyan "react-is": ">=17.0.2" means that you are using the latest version of react-is, which is 19.0.0.

But you are using react 17.0.2. As eps1lon says, you must match your React version. If you change react-is to version "17.0.2" it will work.

[JulCyan]

@Mathias-S See my two examples, on <19.0.0, It means before released 19.0.0, I can not match, of course I know what happened, But It seems a bug, I already accepted this propose, And eps1lon can close it

[zombieJ]

react do the break change of $$typeof, which means when use React 19, the react-is must be the React 19.
But the deps lib which support React 18 is still using the react-is@18.x, so it will never work together if deps lib use old version react-is.

I guess the best way is not to use react-is if need compatible with both 19 or 18 blew and copy the code to realize self.

[JulCyan]

@zombieJ Thank you for your advice. I got the answer I wanted.
If you would like, I want to know how to get this info
Find the break change Logs or looking for this source code?