I guess this comes down to personal preference. For me, this is mixing the interface with the implementation. You shouldn't need to know how something works to be able to use it, for me, that's the real overhead. Maybe this works on a small scale, but what if the source code changes?

That being said, I do like inspecting the source from time to understand it better, or make up for missing documentation. Sometimes though, with this being JS, I wish that I could unsee the things that I've seen, code that production depends upon, deep within the dependency tree.

I agree with the idea of fluency when writing without types, but for me it's not about how fast you can write code. Code for me is a lot of rereading and understanding what the hell you wrote just a few days ago, I find typed code easier to get back into and it's faster to find things that broke in parts of the codebase that you're less familiar with when you change something.