[reverentgeek]

True, it's not the same kind of leaky abstraction you find with other technologies. I'm thinking more about the newcomer to JavaScript/TypeScript, who has only focused on the latest language features, trying to get a grasp of what is going on in the ES5-compatible code that gets generated.

Same is true with relying on Babel, of course.

[WorldMaker]

More so than any random Babel preset someone might hand a new developer, though, Typescript has been pretty strict at this point towards staying strictly to ES Stage 3+ proposals. (And the few exceptions [enums, namespaces] are all common JS patterns that just about anyone should recognize the generated code, and are easy enough to avoid if you want to be more strictly ES Twenty Xteen+Types.)

(Also, the current Babel wisdom of "last two browser versions" suggests that ES2015 or ES2016 is the compatible downlevel of choice in 2019, rather than ES5.)