Cannot assign to read only property 'exports' of object '#<Object>' after upgrading to v5

[piotrblasiak]

Subject of the issue

After upgrading to v5, webpack build completes successfully but in both safari & chrome I get:

Uncaught TypeError: Cannot assign to read only property 'exports' of object '#<Object>' at Module.<anonymous> (client.js:25838) at Module../node_modules/is-plain-obj/index.js (client.js:25846) at __webpack_require__ (client.js:833) at fn (client.js:130) at Object../node_modules/unified/index.js (client.js:113755) at __webpack_require__ (client.js:833) at fn (client.js:130) at Object../node_modules/react-markdown/lib/react-markdown.js (client.js:76128) at __webpack_require__ (client.js:833) at fn (client.js:130)

Your environment

• OS: macOS Big Sur 11.0.1
• Packages: Webpack 4.44.2, react-markdown 5.0.3
• Env: Chrome 87.0.4280.88, Safari 14.0.1

[ChristianMurphy]

@piotrblasiak could you fill out the full issue template? https://github.com/remarkjs/.github/blob/main/.github/ISSUE_TEMPLATE/1-bug.md
This isn't enough information to go off of.

I suspect this is a variation on #518, #514, and #492
but it's hard to tell without more concrete information on your environment and setup.
In particular a minimal reproducible example would help.

[ChristianMurphy]

Closing this as the issue can't be reproduced.
If you have time, feel free to follow up with more information on reproducing the issue, and this can be revisited.