Standardize on error codes for errors express throws

[jonchurch]

Capturing an idea we've talked about offline.

It would be great to move to using (and documenting) explicit error codes for errors that express itself generates, to allow folks to use them as a contract if they wish. That would free us up from having to worry that someone is matching on error messages themselves, and therefore making error messages part of the semver contract with users.

to jog memories, this came up recently when discussing #6756

We don't have all that many tbh, but here's a table I had claude make w/ sites where we generate an error:

File	Line	Error	Proposed Code
response.js	67	Invalid status code: ... Status code must be an integer.	ERR_INVALID_STATUS_CODE
response.js	71	Invalid status code: ... must be greater than 99 and less than 1000.	ERR_STATUS_CODE_OUT_OF_RANGE
response.js	386	path argument is required to res.sendFile	ERR_MISSING_ARG
response.js	390	path must be a string to res.sendFile	ERR_INVALID_ARG_TYPE
response.js	400	path must be absolute or specify root to res.sendFile	ERR_INVALID_PATH
response.js	681	Content-Type cannot be set to an Array	ERR_INVALID_ARG_TYPE
response.js	755	cookieParser("secret") required for signed cookies	ERR_COOKIE_SECRET_REQUIRED
response.js	936	Request aborted	ERR_REQUEST_ABORTED
response.js	946	EISDIR, read	ERR_EISDIR
request.js	66	name argument is required to req.get	ERR_MISSING_ARG
request.js	70	name must be a string to req.get	ERR_INVALID_ARG_TYPE
utils.js	148	unknown value for etag function	ERR_INVALID_OPTION
utils.js	180	unknown value for query parser function	ERR_INVALID_OPTION
view.js	61	No default engine was specified...	ERR_NO_VIEW_ENGINE
view.js	84	Module "..." does not provide a view engine.	ERR_INVALID_VIEW_ENGINE
application.js	213	app.use() requires a middleware function	ERR_INVALID_MIDDLEWARE
application.js	296	callback function required	ERR_MISSING_CALLBACK
application.js	562	Failed to lookup view "..."	ERR_VIEW_NOT_FOUND

Fastify does this quite well already: https://fastify.dev/docs/latest/Reference/Errors/

[efekrskl]

We should definitely do this. I was recently going through the codebase, and our errors messages are really inconsistent 😅

Should we also brand our errors like Fastify does? (e.g FST_xxx)

[sanwalsulehri]

I am interested to work on this

[byteforge38]

Hi @jonchurch , can you assign this issue to me?

[jonchurch]

This is in the discussion phase currently so Im not planning on assigning it to anyone outside the core team currently 🙇

[Delapouite]

Related: a new TC39 proposal has recently been created to officialize the error.code property:
https://github.com/jasnell/proposal-error-code-property