Great challenge. It took me some time to get the mathematics for the decoder.

Not a kata suggestion. See https://docs.codewars.com/training/troubleshooting#post-discourse.

Not an issue, a question. But you can keep discussing your current problem.

You sure that's the input and not your result? You can print the string and the rail number at the start of the function, y'know.

"ABCDEF" decoded to "GHJKLM" seriously?

Well, you're given the number of rails which should help you decode the input string back into normal again.

in JS: expected 'WEIEWEIEWEIEWEIEWEIEWEIEW' to equal 'WEAREDISCOVEREDFLEEATONCE'
How should a final result be obtained from such a set of characters???

Very tricky kata, keep it up, many congratulations.

The tests are fine, your code fails some tests like the ones with an empty string:

For both encoding and decoding, assume number of rails >= 2 and that passing an empty string will return an empty string.

expected +0 to equal ''

Check your code, not a kata issue.

my encode and decode should work correctly but there is a test cases which got a spaces and i handled them but still there is an errors, you might need to look at it

Very good Kata! Thanks to author!

Encode is the easy part, decoding is harder

Make encoding: 15min.
Make decoding: 2h.