Think of the change as a statically compiled language writing parts of their runtime with assembly or unsafe pointers. It’s not an indictment of TypeScript.

I have a hard time believing that. We have 10k lines of typescript and that take forever to compile compared to 5x more of the ReasonML code we have that compiles instantly

If your memory is good, I'm impressed.

> It did take quite a bit of discipline, but with a skilled team it really wasn't all that hard.

Out of curiosity, what was the turnover within the team? My personal experience is that static typing helps a lot when you're new to a codebase. Probably less so when everybody can recite the architecture in their sleep.

> The biggest downside was the lack of automated refactoring tools

That's what a typechecker gives you–an automated enforcement mechanism for ruling out certain errors during refactoring.

This certainly depends on what the code does and on the use case, i.e. on how critical reliability and performance are. 10k code in a simple web application prototype that will be trashed in 3 months is not "a lot", because it's not critical and piling up technical dept is not a problem. 10k code to specify the core algorithms in a mission-critical, long-living system is "a lot", or at least "much more", because it needs to be crafted and maintained with immense care.

Unless one is paid in LOC I'd expect a senior dev to write less code than a novice...

It's enough to benefit from types, assuming no large swathes of inline literals.