A Global Catastrophe
No var; no let; no const. That can be done outside of any Ruby method or JS function, as seen above, or it can be done within such confines.
But let’s take a look at the SCOPE of variables y and ruby_y.
The scope of such a variable is global, whether the programmer intends it or not. Forgetting to declare it with a keyword; a perfectly innocent mistake, especially for someone trying to transition over to JS from Ruby… not that I ever have… because I HAVEN’T!