Document default host for app.listen()?

[karlhorky]

Hi, first of all, thanks so much for Express and the ecosystem, very foundational project! 🙌

Just wanted to ask whether the Express team would be open to maintaining a sentence in the docs about what the default values are for host when using app.listen() with only a port. Currently, in the Express 4 and 5 docs, only the behavior of an omitted port argument is documented - the behavior when omitting the host is not mentioned:

1. Express 4 docs for app.listen()
2. Express 5 docs for app.listen()

Maybe something similar to the Express 2.0 docs (maybe also with a disambiguation of INADDR_ANY):

When host is omitted all connections will be accepted via INADDR_ANY.

https://expressjs.com/2x/guide.html#:~:text=When%20host%20is%20omitted%20all%20connections%20will%20be%20accepted%20via%20INADDR_ANY.

I guess this issue contains one of the closest descriptions of the behavior here:

• Hello world example contains misleading binding information #1318

[dougwilson]

We can document it, though the behavior is whatever the version of Node.js you are running is. For Express 4, that is Node.js 0.10, all three io.js, and up to currently Node.js. I you can confirm all of those have the same behavior when host is omitted, we could add whatever that behavior is to our docs (but probably add that it could change with future Node.js versions, regardless if you didn't upgrade your Express version).