composing-examples.js

const g = n => n + 1;
const f = n => n * 2;

const trace = label => value => {
  console.log(`${ label }: ${ value }`);
  return value;
};

const doStuff = x => {
    const afterG = g(x);
    trace('after g')(afterG);
    const afterF = f(afterG);
    trace('after f')(afterF);
    return afterF;
};

const pipe = (...fns) => x => fns.reduce((y, f) => f(y), x);

const dostuffPiped = x =>
    pipe(
        g,
        trace('after g'),
        f,
        trace('after f')
    )(x);

doStuff(20);
dostuffPiped(20);