app is undefined in configureServer

[DryaginMihael]

Current behavior

I need to register middleware and use this documentation. My project has react-styleguidist@13.1.4 and webpack@5.98.0. I added the configureServer function in styleguide.config.js, but I get the following error: TypeError: Cannot read properties of undefined (reading 'get') when starting the project via the styleguidist server.

Thoughts:
There was no issue with react-styleguidist@11.x because it used webpack-dev-server@3.x, which was based on express. However, after react-styleguidist@12.0.0, webpack-dev-server was updated to version 4.x, which no longer works on express but uses http.createServer instead. This is why devServer.app does not exist.

To reproduce

1. clone fork repository https://github.com/DryaginMihael/styleguidist-example
2. checkout to branch issue-demo (main changes here)
3. run npm run start
4. you got error, server did not start

Expected behavior

• No error should occur when starting the project.
• app should be defined.
• I should be able to register middleware.