I agree with you but we were talking about Dart vs Typescript. ES6 is fine if you’re sketching something and wanting a flexible (i.e. subject to change) view of something, if you have a clear/certain design there are far better systems than building the most complicated type system that both the OP and the GP can’t tell are truly type safe? Why on earth would you choose to build your type safe system in something this broken? If you don’t understand why the other systems are better that’s fine but I think try doing Golang, then Lisp, then Haskell, then maybe Elm or even Dart you’ll see that Typescript is just a lie that causes huge amounts of extra work on top of your usual work. Just my opinion but the effort/reward/beauty ratio is all wrong in TS.

I have used Dart's type system and prefer it to Typescript because it's much simpler and better integrated into the language. I think "dynamic" is better than "any" because the type is inferred by dart which gives more type safety than Typescript does here. Obviously TS won't have a clue what to do after an "any" is passed into another Type afaik?

You are right that that checking for nulls is a bit weird but you just set default values using ?. and. ?? and get on with your life - it doesn't make the whole type system bad and there will be attempts to fix this in the future.