The main benefit of purely functional systems is function composition. The ability to build entire programs through the composition of function primitives. Composition without dependencies.
The problem with javascript is that this concept is entirely lost on react developers. Due to the untyped nature of javascript and it's close linkage with html. HTML is made up of dependent components and this essentially puts dependency injection into javascript leading to JAVA like issues that the functional paradigm was suppose to solve.
It's complicated because nobody knows how to fix it. There's no formal definition for a "good design" or a "better design", so people keep iterating over the designs not knowing whether the new design is actually better or worse.
If there was a way to quantify a good design vs a bad design through an algorithm then people can iterate in ways that properly and categorically makes things better rather than in ways that are opinionated, vague and possibly even in the wrong direction.
What if I told you there is a theory about good module design and if you follow the formal rules of the theory (not design principles mind you there's a huge difference) good and organized designs can emerge from just knowledge of the theory itself?
Any lifetime that depends on an io loop or user input cannot be determined within the loop Period. Even if you have an asic designed for garbage collection. It cannot even be dynamic.
Basically in these cases you have to extend the lifetime to beyond the point of indeterminism into the point of determinism or in other words move the life time outside of the loop.
Worst case scenario you move the lifetime to right before termination of the program.