This involves deep React runtime compatibility issues between dev and prod modes.
The issue reports incompatibility between React 19 dev and prod builds when used together in micro frontend architectures, which worked in React 18. This appears to be a core runtime behavior change that would require React team investigation, as evidenced by multiple complex workarounds from the community.
Unable to run multiple React micro frontends (MFEs) when they don't all use the same NODE_ENV. When developing large systems using micro frontends (e.g. via module federation), it is not feasible for developers to have every MFE running locally. Instead, a proxy config can be used to pull built artifacts of existing MFEs and only run relevant apps locally. This worked well in React 18, but does not in React 19.
React version: 19
Link to code example: https://github.com/rdenman/react-19-mixed-env-mf
Unable to run mixed builds (dev + prod)
Both dev and prod builds should be compatible.
This is the error I see when running the attached example. Note that downgrading the example to React 18 fixes this issue, and running both apps in either dev or prod mode also resolves the issue. <img width="705" alt="Screenshot 2025-01-08 at 7 59
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