I am going to close this issue as a user error. If you are really, really sure your code is correct, plese post here:

• your code (formatted and marked as spoiler),
• input of failing tests,
• failure message, and/or value returned by your code and value expected by tests.

You can also come to #help-solve channel of Codewars Discord, someone will definitely help there.

Your solution seems to return invalid, too small values:

Testing for 4440220
   It should work for random inputs too: expected 4440022 to equal 4442002

expected 1234567089 to equal 1234567908 - my code produce correct: 1234567098

This does not seem to be the case. After adding logs to your solution, I can see:

Input:1234567890
Your result: 1234567089
   expected 1234567089 to equal 1234567908

Your code does not produce 1234567098.

The kata does not ask about the biggest.

2017 can be 7210.. 2071 is not the biggest
or
Expected 123456798 but got 987654321
how woud a number starting with 1 be smaller, when it contains 9 ?!

B1ts, thanks you, I saw an error) I was wrong)

Spend some time yourself, because everything is correct, apart from your code.

replace let n1,n2 on const, === on ==