Most definitely not. It's not allowed in Python, it's not allowed in Ruby, it's not allowed in any Lisp I know of[0], … it is allowed in PHP, which is about what I'd expect from that[1]. In most dynamic languages the arity is not a suggestion[2].
Which is exactly the issue at hand: `Array#map` was (stupidly) defined as calling its callback with 3 parameters. The last 2 are useless 99.99% of the time (and in better language you'd compose them in if and only if you needed them), as a result it's almost universal that you'd pass single-parameter callbacks which works… until it doesn't because the callback now takes 2+ parameters and starts taking in account the previously ignored garbage `Array#map` feeds it. The average JS developer likely doesn't even know Array#map callbacks receive 3 parameters, and usually aren't going to think about it: in 99% of cases it's has no relevance whatsoever.
[0] but most lisps make significant uses of variable-arity functions, which is a very different and much more formal proposition
[1] PHP's one saving grace being that HoFs have historically not been much of a thing, though I have not tracked how it's used these days
[2] as long as it's present at all AFAIK in Perl functions don't have formal parameters lists
def hello(a, b = 'world'):
print(a, b)
hello('hello')
hello('hello', 'world')
hello('hello', 'world', 'there)
# nor
def hello(a):
...
hello('hello', 'world')In python those functions would look like:
def F(a = None, b = None, *args): ...