Who Provides The Next() Function In Express Middleware?

I'm confused about how next() works in Node.js and Express middleware. There have been some other questions about middleware works, for example here, but I'm looking for a differen

Solution 1:

An Express application is essentially a series of middleware calls.

Middleware is a function with access to the request object (req), the response object (res), and the next middleware in line in the request-response cycle of an Express application, commonly denoted by a variable named next.

As written above, Expressjs provides the next callback function. Next is just a way of calling the next middleware in the flow.

For many examples see Express's Using middleware