Is an intermediate event handler also middleware or not?

Question

Express.js

It is clear what midlware is, this is the code that is executed between the request and the response, it has access to the request and response object, etc. but in the code I once met a code like this

app.get('/',  (req, res, next) =>) 
// to do
next(err)

Is it an intermediate event handler?
But the question is how does it differ from middleware which is in app.use(...)?

Answer 1

Nothing, it's all middleware. The essence of the intermediate handler is that it must be called at the very end and either terminate the process or pass req / res objects to the next intermediate state.
Here you can see the implementation inside express, and here you can read how the whole thing works