Having worked on large backend codebases in both TS and JS, the difference is stark. The TS API in my case had something like 90% less errors, and those were all subtle bugs in business logic.
On the other hand, the large JS API over time had all sorts of unexpected type errors and undefined behavior. I'm aware that this is anecdotal evidence, but TS is pretty much a no-brainer now on backend.
I have no experience with maintaining TS projects over a longer period of time, but I have started some experimental TS projects where I was looking for type declarations.
What I found didn't seem to have any formal reference to a specific version of the library. I found that a bit scary. Not sure if it actually causes problems though.
So it's not that it's a source of errors as most libraries are backwards compatible.
It can be. But most popular libraries have very good version syncing, or even include definitions in the module itself. In the worst case, or if there are no typings available at all, you can just import the plain js, and use it untyped, which can be acceptable if it is not used in a lot of places.
> didn't seem to have any formal reference to a specific version
Yeah. It mostly works if you install the latest version of them both at the same time. Sometimes I've had to fiddle with backing the definition or the module back a version to get them to match.
That sounds like a red flag to me. I hardly have any type related bugs in my pure JS server code. Must be a poor developer in the team. Too easy to blame JS for that.
If TypeScript let's that developer make good code, then the variable is JavaScript.
When the tools help you, a good developer can focus on making better things rather than not making mistakes.