I see. Thank you.

Sergio, this returns true when divisors x and y leave the same remainder, right?
e.g. (11 % 2) == (11 % 5) // (1 == 1) true
but 11 is divisible by neither 2 nor 5, and should return false.

Oh thanks i didn't even think about it as unsafe. Just learned it from 'reverse string challenge' with limited characters. And this kumite is honestly, but a test. Was wondering what is this, found out after submitting. I'll find a way to delete it, i guess.

You basically defined a function without any declaration. I feel like you should know the many dangers involved with that practice. Check out this link for more information.

https://www.sololearn.com/Discuss/2191625/javascript-arrow-functions-with-and-without-const

Wanted to extend the idea of using default parameters. I wish I could keep the spread operator, but it must be the last, and default params are set left to right.

e=>e can be replaced with Boolean

Sometimes I am just wondering, how beautiful JavaScript is - and how many clever people are there. And at the same time, I am also happy that I do not have to maintain this kind of codes :D Hope you do not use this kind in production! Anyway, hats off for this math/algo skills :)

The function should not return {} for invalid inputs, otherwise the output for valid/invalid inputs is indistinguishable.

Fixed tests are too weak. At least tests with booleans, non-empty arrays, objects having arrays/empty strings/0's as values should be added.

No random tests.

Excuse me but who upvotes this as a best practice :D