pre:error event in createApp

[JedWatson]

cc @snowkeeper, @creynders

There's currently no way to hook your own error handling middleware into the express app if you're using redirects (e.g. for custom 404 pages). I'm going to add a pre:error event to handle this.

Not 100% sure how best to hook in an actual custom error handling method though (i.e. one that takes 4 arguments: err, req, res, next) - this has special behaviour in express and isn't the same as a 404 handler.

Maybe the best way would be to add both pre:notfound and pre:error events, but in that case the "pre" doesn't actually make a lot of sense unless you read it as "run this before the generic handlers for notfound / error conditions"

I'm also a bit skeptical about the value of taking this much control over the express stack by default... it's really not that hard to configure in your project anyway, and the only reason not to just add these to the end of your routes(app) handler would be if you're using the built-in redirect functionality. Maybe a better answer is to back-track a bit here.

Feedback welcome.

[webteckie]

This one I'm having a hard time understanding! For sure I'm missing context or knowledge :-)

[creynders]

Errr... Nope, I can't grok it either.
So, the use case is: a developer wants to be able to intercept 404 errors for instance, i.e. /keystone/nothinghere and they want to respond to that? Or are there other use cases as well?

[bassjacob]

@JedWatson is this still a feature request to consider?

Would this be an error handler that runs only in the userland app, or also the admin app?

[gautamsi]

not sure if this is still relevant, closing as no activity for long.
given that Keystone 4 is going in maintenance mode (see #4913 for details). chances for adding new features are minimal.