They've discovered how to write dynamically-typed code correctly, or at least, a philosophy of it. It's not "discovering static typing" because that doesn't come up in static type languages. (Typescript is, for this particular purpose, still effective a dynamically typed language.)

I remember writing Python and Perl where functions largely just aimed you passed them the correct types (with isolated exceptions where it may have made sense) years before JavaScript was anything but a browser language for little functionality snippets. It's a dynamic language antipattern for every function to be constantly defensively checking all of it's input for type correctness, because despite being written for nominal "correctness", it's fragile, inconsistent between definitions, often wrong anyhow, slow, and complicates every function it touches, to the point it essentially eliminates the advantages of dynamic language in the first place.

Dynamic languages have to move some responsibility for being called with correct arguments to the caller, because checking the correctness of the arguments correctly is difficult and at times simply impossible. If the function is called with the wrong arguments and blows up, you need to be blaming the caller, not the called function.

I observe that in general this seems to be something that requires a certain degree of programming maturity to internalize: Just because the compiler or stack trace says the problem is on line 123 of program file X, does not mean the problem is actually there or that the correct fix will go there.

I thought parent commenter was making a joke but thanks to you I am not sure anymore.