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