It works and is IMO quite okay because NA is not the same as NaN (not a number). NA _does_ actually stand for a number, it's just that we don't know it.

Which is an interesting detail in R that should be mentioned anyway, the difference between NA and NaN. Anyone used to languages which just NaN may confuse NA for that non-value.

https://www.r-bloggers.com/2012/08/difference-between-na-and...

https://cran.r-project.org/doc/manuals/r-release/R-lang.html... (lots of details how NA and NaN are handled)

Except - 1^NaN also is 1... now that IMO is wrong. But you can try the same in your browser's JS console and you will get 1 as a result too, so R is not the only one.

There are several NA values in R - NA_integer_, NA_real_, NA_complex_ and NA_character_, and the results will be different if you use some of them. NA_character_ and NA_complex_ will produce errors (different ones).