NodeJS / Express: what is “app.use”?

Question

In the docs for the NodeJS express module, the example code has app.use(...).

What is the use function and where is it defined?

Answer 1

app.use() works like that:

1. Request event trigered on node http server instance.
2. express does some of its inner manipulation with req object.
3. This is when express starts doing things you specified with app.use

which very simple.

And only then express will do the rest of the stuff like routing.