Your code has 2 problem:

1. You must define function named '', your code doesn't do that, it defined function with single argument called ''.
2. You are missing some * operators (multiplication) - but this is problably result of markdown parser.

Good luck

It is hard to say, please post your source code in replay.

It is probably new-line character "\n". I have updated test, so they return more accurate message.

Sorry for this inconvenience.

I have improved the tests, now they indicate which character is wrong.

To solve this task, it is enought to know some basic ES6 features and JS operators, but used in little strange way ;)

At first, think about how to use this symbols to generate number.

I propose test cases:
??1=?
1??=?

It seems then the problem is in missing require 'prime' statement in test code.

Hi, I get following error:

#
 `sol'
 `block (3 levels) in 
'
 `block (2 levels) in 
'
 `times'

for all random test of ruby solution. What does it mean? Thanks