Of course it would. Patches which improved the documentation would be very welcome.

Also it seems a bit weird to have 'any' and 'filter' without having 'first'.

Not really -- "any" and "filter" are total functions, but "first" of an empty list is undefined.

On the other hand, that also applies to foldl1 and {max,min}imum{,By}, so it's probably not the reason.

The reason is probably that in JavaScript you can just say a[0] to get the first element element of a.

It seemed unnecessary, yes, although I suppose there are possibly some circumstances where one might want a `first` function—for example if one were folding over a list of lists.

There are an infinite number of circumstances where one would want 'first'.

In Lisp terms[1], 'first' is 'car', which, in conjunction with 'cdr'. With that combination recursive logic is regularly implemented.

[1] Some Lisps already include this alias.

In most cases the "a[0]" approach works, however. The set of circumstances where you want "first" as a proper function is limited to those cases where you need to pass it into some higher order function (which is still infinite, granted, but it's not 'every time we'd want "car"').