Functional programming

Compose .js

export const compose = (...fn) => fn.reduce((f, g) => (...arg) => f(g(...arg)));

Curry .js

export const curry = fn => {
  const arity = fn.length;

  return (...args) => {
    const firstArgs = args.length;
    if (firstArgs >= arity) {
      return fn(...args);
    }

    return (...secondArgs) => {
      return fn(...[...args, ...secondArgs]);
    };
  };
};

Imperative - Declarative Function composition .js

// Function composition OR
// import pipe from 'lodash/fp/flow';
const pipe = (...fns) => x => fns.reduce((y, f) => f(y), x);
// Functions to compose
const g = n => n + 1;
const f = n => n * 2;
// Imperative composition
const doStuffBadly = x => {
  const afterG = g(x);
  const afterF = f(afterG);
  return afterF;
};
// Declarative composition
const doStuffBetter = pipe(g, f);
console.log(
  doStuffBadly(20), // 42
  doStuffBetter(20) // 42
);