alt Hacker NewsArticle describes try/finally as a hack to get the effect of defer, but it looks to me like it's the other way around? Try/finally is more traditional, in one form or another.
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It's also necessary here because TypeScript has exceptions and you'd expect your `defer`s to execute even when an exception is thrown.
Finally isn't bullet proof. If you execute a promise in a try block and it happens to end without resolving, the finally block will be never be executed. Fun stuff.
If the idea of computers is that they remember stuff for you and do stuff for you, then both try/finally and defer seem like hacks to work around not having RAII like e.g. Rust or C++ where resources are closed/disposed of/deallocated automatically.
Try X finally dispose of all resources. X, defer clean up X. Or how about just X and cleanup is done automatically, with the author of the resources deciding what is needed to clean X up.
A (lexically-scoped) defer is a more general than a finally block. You can express finally-block semantics using defer.
It's also more exception-safe when you have more than one throwing call in the try block.