TIL that Javascript engines optimize out unused variables available in outer lexical environment if they aren't used inside nested functions.
Earlier I used to think this is the default Spec behaviour but it's rather an optimization 💡.
In this video, we see how exactly Firefox confirms that for us !!
People really underestimate the power of JS engines, and what you pinpointed in this video is just a spec in a sea of optimizations within those engines. They all utilize cutting edge of optimization techniques, and this example with closures is not new.
Anyway, good video.