add extension swap-errors

[jgirardet]

the swap-errors extension allows swapping response when HTTP Error code is returned.
It's nice way to deal with errors server-side in
It works adding the header HX-SWAP-ERRORS in the response.

[1cg]

@jgirardet do you think that this extension has been obviated by the new support for configuring swap behavior in the htmx:beforeSwap event?

[jgirardet]

No I don't. This extension allows you to write less javascript where htmx:beforeSwap forces to write more JavaScript.
Since many errors are handled server side, I think it's better for htmx to support the result (with a non 200 status code) out of the box.

[vrecan]

I agree, I think this would be extremely useful. It's sad to see that this never got merged.

[alexpetros]

This extension allows you to write less javascript where htmx:beforeSwap forces to write more JavaScript.
Since many errors are handled server side, I think it's better for htmx to support the result (with a non 200 status code) out of the box.

I agree with this, though coming up with a conceptual framework that allows configuration via attributes (instead of JS) is difficult!

We're working with this concept in #1620, so I'm going to close this PR in favor of that.