JavaScript Currying 3 - Compose

The compose function in the code below takes any number of functions, returns a function that takes the initial value, and then uses the reduceRight function to iterate right-to-left over each function f in functions argument and returns the accumulated value y. In other words, the compose function creates a pipeline of functions with the output of the function is connected to the input of the next function.

const compose =
  (...functions) =>
  (x) =>
    functions.reduceRight((y, f) => f(y), x)

const g = (n) => n + 1
const f = (n) => n * 2
const h = compose(f, g)
h(20) // => 42

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