That's because there's no recorded metric for every time a dev working in plaint JS mis-spells a property, or accesses one at the wrong level, calls a function

That's because there's no recorded metric for every time a dev working in plaint JS mis-spells a property, or accesses one at the wrong level, calls a function that doesn't exist on that particular version of the library, etc, etc. For the most part, the resistance to Typescript from devs who prefer to write plain Javascript is purely borne out of adding the types being "too much effort to be worth it". Sure you gotta wrestle with the type system now and then but there's often a reason you have to + once it works it usually works very well. Which I find kind of funny bc those devs don't mind putting the effort into writing unit tests, but adding types (think of them as just lower level tests) is somehow an insult to the way they do things. But nah they'll still just rawdog their JS and just make mistakes/misspell stuff now & then as we all do. Let's just hope tests/CI pipeline is enough to pick it up before it gets to prod.