Upgrade React

[pikariop]

Upgrade React and react-dom to new major version 19

Using v 19.2.4, shadow-cljs compiles but the browser renders a blank screen and prints the following in the console

[pikariop]

Since there was a helpful error message suggesting to use the new reagent.dom.client API, I figured I might do just that and spend 15 minutes looking further into what kind of rabbit hole awaits us.

With these changes https://github.com/CSCfi/rems/tree/upgrade-react-19 ,
I got the application to compile but a number of browser tests fail, and shadow-tests fail to load both locally and on CI with the following message

  Uncaught Error: Target container is not a DOM element.
  at cljs-test.js:193580:9
  
  Error: Target container is not a DOM element.
      at exports.createRoot (cljs-test.js:193580:15)
      at reagent$dom$client$create_root.cljs$core$IFn$_invoke$arity$1 (cljs-test.js:193650:45)
      at cljs-test.js:209648:48

https://app.circleci.com/pipelines/github/CSCfi/rems?branch=upgrade-react-19

Most of the pages seem to render just fine, but when editing the catalogue item it renders a blank screen and the following error message prints into the browser console

Which suggests to me that there might be an incompatibility in the Komponentit library. The current version of Komponentit depends on Reagent version 1.2.

There's an open issue about dropping the dependency altogether (#3009), which might be a good place to start for anyone looking to further this task.