Function Currying

What would be the output of this point-free style code using curried functions?

const map = (fn) => (array) => array.map(fn);
const filter = (fn) => (array) => array.filter(fn);
const compose = (f, g) => (x) => f(g(x));

const isEven = (x) => x % 2 === 0;
const double = (x) => x * 2;

const doubleEvens = compose(map(double), filter(isEven));
const result = doubleEvens([1, 2, 3, 4, 5]);
console.log(result);

[2, 4]
[4, 8]
The output is [4, 8]. This code demonstrates 'point-free' style programming, where function definitions don't explicitly mention their arguments, using curried functions and composition. Here's what happens: The `doubleEvens` function is a composition of two operations - filtering for even numbers, then mapping to double each value. When applied to [1, 2, 3, 4, 5], it first filters out [2, 4] (the even numbers), then doubles each to produce [4, 8]. This style of programming, enabled by currying, leads to concise, declarative code that focuses on transformations rather than intermediate steps. It's a powerful paradigm in functional programming for building data processing pipelines.
[2, 6, 10]
[1, 2, 3, 4, 5]

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