Yes, I get what your saying, but I can implement the map filter and reduce abstractions with a for loop using this accumulator pattern or pass in the paramete

Yes, I get what your saying, but I can implement the map filter and reduce abstractions with a for loop using this accumulator pattern or pass in the parameter by value (aka copy) then modify the original structure. If I can implement MAP using a FOR loop then they are relatively the same thing as I can just replace a MAP with it's FOR loop definition and get the same result. Here's my main point. There is no meaningful change to your imperative program when you replace for loops with maps. The core structure of your code is exactly the same. What you have introduced is a convenience aka sugar. If you were to truly do functional programming the architecture of your entire program will be drastically different from imperative code... To counter the posters original statement: There is a gigantic difference between just using map and reduce in your imperative javascript code vs. actually writing a functional program... It is not a trivial difference. I feel many people who understand javascript fp libraries like underscore think they know functional programming when all their really doing is sprinkling map and reduce all over their imperative code. You guys don't get it yet, and you'll never get it if you keep coding in javascript. The difference is night and day, it's like SQL vs python.