That is actually pretty clever.

map is a sugar of reduce~

what a map

mind to explain a bit?

Nice because it's also readable.

Interesting solution

Nice! I have a similar solution using reduce, but this is even easier.

No early return by using map if it finds the missing number.
There're some comments about forEach, it doesn't early return, too.

A really clever solution. One downside is that there is no early return, meaning that it will loop over every single value in what could be a very large array, even if a missing number has already been identified.

Yes, forEach would be more appropriate in this instance as the iteration doesn't need to return anything.

I did mine like in the top rated example but I like this more.

for is more suitable I think.