The issue I see a lot in the JS ecosystem is laying out documentation like a reference guide, but then not including all parameters or functions. These types of documentation are very helpful if what you need to know is included, because they have nice friendly explanations and examples. But eventually you will run into a parameter that is mentioned on Stack Overflow, or is in a code snippet in the documentation, but then has no further explanation in the documentation, as if it doesn't exist.

Projects where the README is the only documentation seem to suffer from this problem the most. They give examples of the most common parameters and functions, and then that's it.

In JS this is a big issue because there may be no way to know a parameter even exists, or what values it accepts, unless it is documented.

A lot of documentation in the Java ecosystem has huge auto-generated monstrosities with absolutely no explanations. In Java this is usually not useful because that information can be found in the types. But in JS it would be incredibly useful. Unfortunately it isn't as easy to automatically generate that type of documentation for JS.

Python in my experience has the best of both worlds. It has the friendly explanations and examples. But also has all of the parameters, even if explanations for some are a bit less detailed. And all of that is combined into a single place.