functional programming is a programming paradigm — a style of building the structure and elements of computer programs.
it returns the same result if given the same arguments (it is also referred as deterministic).
It does not cause any observable side effects.
The code’s definitely easier to test. We don’t need to mock anything.
Unchanging over time or unable to be changed.
if a function consistently yields the same result for the same input.
is just essentially anther javascript files
include modules that exist in separate files.
using ‘require’ function.
do same module export equal to what ever we want to be made.