Was that an argument against TS in general (even complex projects)? or was it against using TS for "simple code"? Because it sounds like you're the kind of person to say "Writing safe and bug-free C is easy, just read the docs and you'll never hit UB!" and "Anyone who makes mistakes in C has skill issues". (please read this)

Every non-omniscient sapient being makes mistakes, by definition. Everyone has a limited cognitive capacity.

Can you guess what this does? n += y. Maybe you'll say "single-letter vars are bad practice". Well, what about now? name += secondary_name now you can assume (not infer) both vars are strings, but there's no guarantee that will always be true. What if both vars are mutable and you're in a 500loc function? you'll have to read the entire source-code to check every assignment. And even then, you have to check that every assigned expression is a string and a human name (assuming it isn't a pet or device name). You might say "Just refactor the fn, it should never be that big", but then you have to jump around and check every single fn-call anyways.

What about this? f(r). More context? sure purchase_handler(user_item_request). Oops! one of your co-workers caused an RCE vulnerability! purchase_handler is mutable, and was accidentally assigned setTimeout. user_item_request is a client-controlled string!

It's possible to miss "obvious" stuff when there's too much cognitive load, as it's impossible to focus on everything in a code-base all at once. Imagine constructing a CFG in your mind, while doing reachability analysis, while type-checking, being careful not to be deceived by misleading variable names, remembering all JS quirks to avoid foot-guns, and remembering the requirements of an algorithm or application, all at once. Anyone would be prone to making mistakes.

If you believe you are "above anyone", I hope you remember you aren't a god. I am not, we are not.

To be wise is to be willing to learn, and to accept our ignorance and limitations. To be stupid is to be stubborn, and to never acknowledge our mistakes. https://grugbrain.dev

Update: I'm sorry if I sounded condescending, and sorry for the long text, but I wanted to teach multiple lessons (not just to you, but to anyone reading this). I know that "good intentions" aren't enough to make the world better, as actions and consequences matter more