I think this wording could be improved. I understood this rule to mean that the loop wouldn't have 1 follow 9, unless there was a 0. Therefore: 901 would be good, but 912 would not.

A second sentence like this one would help: "a sequence will not roll over after the last digit, so 1 will never follow 0"

I think you're correct. 109 is interesting, but it's entered as a test case for "close to interesting" (output=1). 109 matches the pattern for the decrementing sequence: 0 comes after 1, but not before 9. Therefore: 2109 and 321098 would also be interesting numbers.

This is clever! However, I recently read that the eval() function is a big security risk and is not advised under any circumstances anymore: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval#never_use_eval!