Version

3.0.0-rc.3

Reproduction link

https://webpack.js.org/configuration/dev-server/#devserver-before

Steps to reproduce

Add:

devServer: { before(app, server) { server.sockWrite(server.sockets, "content-changed"); } } 

to vue.config.js file.

What is expected?

sockWrite method on server is hit successfully

What is actually happening?

server is undefined