What is function composition and how do compose() and pipe() differ?

Function composition combines multiple functions where the output of one becomes the input of the next, building complex operations from simple pieces.

// compose — right to left (mathematical convention)
const compose = (...fns) => x => fns.reduceRight((v, f) => f(v), x);

// pipe — left to right (more readable)
const pipe = (...fns) => x => fns.reduce((v, f) => f(v), x);

const trim      = str => str.trim();
const lowercase = str => str.toLowerCase();
const addBang   = str => str + '!';

// compose: addBang(lowercase(trim(x)))
const processC = compose(addBang, lowercase, trim);

// pipe: trim → lowercase → addBang
const processP = pipe(trim, lowercase, addBang);

processP('  Hello World  '); // 'hello world!'
processC('  Hello World  '); // 'hello world!'

// Without composition (harder to read as chain grows)
const manual = str => addBang(lowercase(trim(str)));