> so would you say that one of the first things a htmx based project should do is handle all the error conditions ? like all the 40x and 50x ? and stuff like your modal thinggy ?

IMO yeah, but different pages and actions will (probably) want different things. For example clicking a button that makes a POST request may make more sense to have a red toast notification if it fails, however a tab that dynamically loads its content in using htmx might want a dummy placeholder saying "Sorry, try again later" or something like that. Functionality around the modals were done as and when we needed them and then expanded on over time so I don't think you need to write/know everything up front. It's honestly been a joy to use based on how simple it is once embrace server side rendering.

> how do you develop the js here ? do you setup a different nodejs/npmjs toolchain. or do the jqueryish development of edit->browser reload ?

For my projects it's just 1 or 2 JS files that are included in my base template that contain the event handlers, so it's quite old school of edit and refresh. I use Django mostly now so I can use that to collect and minify static files so it's low effort/complexity.

The only down side is for the few JS packages I do need (e.g. Select2 for nice dropdowns) I either vendor the package in (no automatic updates) or use NPM (but it's a pain). Again, depends on what you want because htmx doesn't care either way.