You mean these? Does it use them internally, because I haven't really seen them in any Svelte code.
If so, what does it matter what the compiler does in order to make your code work, so long as it's legal? It's perfectly valid JS, that's all that counts.
I wouldn't say Svelte is weird as much as it's different. That's the whole point after all. Instead of adding a bunch of library bloat and keeping an entire copy of the DOM to constantly compare to and derive changes from, it compiles your components down to native JS that manipulates the DOM directly, like you would by hand. Except of course the compiler uses different ways to achieve that than you would, but that's because it doesn't have to care about readability, as long as it creates valid and efficient code.
I'm coming back, I will return
And I'll possess your daemons and make your CPU burn
I have ring 0, I have your cores
I have the power to make my evil take its course
Well yes, internally that's what it does, but from a user perspective it just looks like being handed the package, you never see any of the failed attempts (unless delivery fails completely because the company went out of business). It's sorta more like having a butler who orders it for you and deals with any potential BS that might happen, and then just hands you the package when it finally arrives in one piece.
It's not like your colleagues will be keeping track of how much time they've wasted writing ineffective code. If anything, they'll try to hide that by arbitrarily inflating sprint points etc.
I've worked in environments like that and the issue almost always isn't that people wouldn't LIKE it if there were tests, it's that they
Don't want to have to learn something new in order to do the same job they're already comfortable with
Are worried that if they convince management to let them invest X amount of time into doing something that will improve productivity, they'll be expected to be more productive in the future
And of course, all of this for no extra money. Unless you work at a place where management prioritzes developer happiness over how many sprint points the team can knock out every week (and those are rare), the sad truth is that it'll likely be about as popular as leftover food growing mold in the community fridge.
Or an Adafruit, perhaps?