playFunctional.js

// Playing around with currying and composing

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

  return function _curry(...args) {
    if (args.length < arity) {
      return _curry.bind(null, ...args);
    }

    return fn.call(null, ...args);
  };
};

const compose = (...fns) => (...args) =>
  fns.reduceRight((res, fn) => [fn.call(null, ...res)], args)[0];

// Data example
const data = [{id:1, name: 'a'}, {id:2, name: 'b'}, {id:3, name: 'c'}, {id:4, name: 'd'}, {id:5, name: 'e'}, {id:6, name: 'f'}, {id: 1, name: 'g'}, {id: 1, name: 'a'}];

// Curried filter functions
const filterById = curry((id,xs) => xs.filter(x => x.id === id))
const filterByName = curry((name, xs) => xs.filter(x => x.name === name))

// Partial application
const x1 = fId(1)
const filteredByX1 = x1(data)
const x2 = fNM('g')
const filteredByX2 = x2(data)

// Reducing without composing
const res = data.reduce((acc, curr) => { return x1(acc) }, data)
const res2 = res.reduce((acc, curr) => x2(acc), res) // => [{ id: 1, name: 'g' }]

// Composing
const kk = [x1,x2]
compose(...kk)(data)  // => [{ id: 1, name: 'g' }]