I don't think this solution is good practice. It's clever. It's efficient (if you need it). But in most projects it's just trick programming that makes code harder to read.

This kata is broken. The test results don't match the tests. I was able to make the tests work by updating the results in assert, but in the "attempt" it failed because again, results don't match the test. Example: "expecte 2 + 8 + 8 + 4 + 0 + 0 to be 6" - wrong test data and results.

Frustrating, as it was the first kata in js.