foo.js

const compose = (...fns) => x => fns.reduceRight((y, f) => f(y), x);
const trace = label => value => {
  console.log(`${ label }: ${ value }`);
  return value;
};
const g = n => n + 1;
const f = n => n * 2;
/*
Note: function application order is
bottom-to-top:
*/
const h = compose(
  trace('after f'),
  f,
  trace('after g'),
  g
);
h(20);
/*
after g: 21
after f: 42
*/