I came across some fancy ES6 javascript code for functions, which were hard/confusing to understand, but slightly shorter.
But the functions seem to be easily written as ES5 regular functions, and more understandable.

"let" instead of "var" does not seem to work?
The coder used a reserve word, "final" as well, which yields an error. Maybe there was a lack of testing.

- Brian

Anything before ES6 doesn’t have the let functionality.