It'd be good to add examples in the instructions (they'll look very verbose but helpful anyway).

Array.prototype.flat() is only supported from NodeJS v.11:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat#Browser_compatibility

Codewars currently uses NodeJS v8.1.3 (you can check the version at the top of the Kata screen: there's a drop down allowing you to choose language + a dropdown to choose the version).

done

I've tried to use the Array.prototype.flat() method in many different katas and for some reason codewars doesn't seem to accept it. I run all my codes no problem on VSCODE but always get an error when trying to use .flat(). Here is the official doccumentation for the method:

https://developer.mozilla.org/pt-BR/docs/Web/JavaScript/Reference/Global_Objects/Array/flat

Node v12.13.0 is not supported in CW yet.

It runs in Node v12.13.0 (on my Mac) perfectly!

Not an issue. This method is not available in any of the supported Node versions.

Your sorting step is wrong.

Thank you

As I finally understood the 11 counted pairs are :

dell & ledl

abc & cba
abc & bca
abc & bac
abc & cab
cba & bca
cba & bac
cba & cab
bca & bac
bca & cab
bac & cab

(JS)
The test is expecting 11 as the answer

[ 'dell', 'ledl', 'abc', 'cba', 'bca', 'bac', 'cab' ]

How can there be 11 anagrams, when there's only 7 words?