transducer-api-transducers-v2.js

import { filterT, map, mapT, pipeT, takeT, transduce, where } from 'nanoutils';

const isEven = value => value % 2 === 0;

const filterPredicates = {
  name: ({ author }) => name => author === undefined || name === author,
  timestamp: ({ from, to }) => timestamp =>
    from === undefined ||
    to === undefined ||
    (from <= timestamp && timestamp <= to)
};

const pushReducer = (arr, value) => {
  arr.push(value);
  return arr;
};

const transducers = (posts, filters) => {
  // iterates over filters and specifies filter values
  const specificFilters = map(filter => filter(filters), filterPredicates);
  // creates validation using Object mapping with post
  const withFilters = where(specificFilters);
  const transducer = pipeT(
    // applies filters
    filterT(withFilters),
    // takes first post
    takeT(1)
  );
  // iterates over posts
  // applies pusReducer to prevent recreation of new arrays
  // starts from []
  // gets values from posts
  return transduce(transducer, pushReducer, [], posts);
};

const posts = [
  {
    name: "Lorna Stiedemann",
    title: "Fugiat qui maiores illo.",
    timestamp: 1534534191881
  },
  {
    name: "Joel Will",
    title: "Ea consequatur eveniet ut qui et quae voluptatem.",
    timestamp: 1531221363376
  },
  {
    name: "Quincy Vandervort",
    title: "Rerum odit nemo in.",
    timestamp: 1535462116340
  }
];

transducers(posts, { author: "Joel Will" })                              // [{ name: 'Joel Will', title: 'Ea consequatur eveniet ut qui et quae voluptatem.', timestamp: 1531221363376 }]
transducers(posts, { author: "Joel Will", from: 0, to: 1531221363370 })  // []
transducers(posts, { from: 0, to: 1535462116340 })                       // [{ name: 'Lorna Stiedemann', title: 'Fugiat qui maiores illo.', timestamp: 1534534191881 }]