transducer.js

const dates = [
  '2018-06-10',
  '2013-03-21',
  '2010-08-03',
  '2016-02-05',
  '2019-06-17',
];

const toDate = d => new Date(d);
const extractYear = d => d.getFullYear();
const isEven = n => n % 2 === 0;

function composeReducer(...fn) {
  return function(reducer) {
    return fn
      .reduce((composition, transform) => transform(composition), reducer);
  }
}

function mapper(transform) {
  return function(reducer) {
    return (xs, x) => reducer(xs, transform(x));
  }
}

function filter(predicate) {
  return function(reducer) {
    return (xs, x) => predicate(x) ? reducer(xs, x) : xs;
  }
}

const evenYearsReducer = composeReducer(
  filter(isEven),
  mapper(extractYear),
  mapper(toDate)
);

const evenYears = dates.reduce(evenYearsReducer((xs, x) => xs.concat(x)), []);

console.log(evenYears);