Chai has unfortunately been left behind by its maintainers. My own personal attempts to contribute were met with silence and oddly-placed resistance (when I was able to get a response). It's been my opinion for a few years that Chai is obsolete tech, but it's still prolifically used in a lot of packages/libraries/etc that are in maintenance mode. There are just a lot of better alternatives now.
What alternatives do you like?
I really enjoy Ava [1] or anything assert-tape-like [2]. "uvu" [3] is getting a lot of love lately, but it's very feature limited and much of it's touted advantages are at the detriment to feature set.
[1] https://github.com/avajs/ava
[2] https://github.com/substack/tape
[3] https://github.com/lukeed/uvu
Jest is great for front-end (or full stack integration) testing, but I feel it's specialized for that use-case and doesn't always play nice with backend/middle-tier testing needs.