My biggest gripe with CoffeeScript, beyond it's scoping being madness [1], is it made writing very inefficient JavaScript much easier. The language was full of footguns.
Many times something would look perfectly reasonable in CoffeeScript but when you would actually read the JS it would be iterating the same dataset multiple times to grab individual items that could have and should have been a single loop.
It's the Hibernate problem all over again. Any time one language is layered on another, the user is totally unaware of the degenerate cases that they are triggering, and the higher language is usually blocked from fixing those. Similar to C++ preprocessors which generated poor C.
Many times something would look perfectly reasonable in CoffeeScript but when you would actually read the JS it would be iterating the same dataset multiple times to grab individual items that could have and should have been a single loop.
1. https://donatstudios.com/CoffeeScript-Madness