Cooooool! But in the last code snippet: You're printing array keys. Must use for of instead of for in . And the python version doesn't include stop in the output of range(stop) . 😜

About the last part of this article, I'm pretty sure that no one can use this package without installing react , thus it's not "optional" and must not be marked as so. For example, you could do that if your package would work with both react and preact . In this case neither of them are necessary and the developer might have installed only one of them and shouldn't see any warning.