filter -> map -> reduce

filter_map_reduce.js

function filterReduce(predicate) {
  return function (accum, value) {
    if (predicate(value)) {
      return accum.concat(value);
    } else {
      return accum;
    }
  };
};

function mapReduce(morphism) {
  return function (accum, value) {
    return accum.concat(morphism(value));
  }
}

ClassList.of([
    'btn__background--solarized',
    'btn__text--solarized',
    'btn__overlay--solarized',
    'btn__icon',
    'btn__placeholder'
]).reduce(filterReduce(str => /--solarized/.test(str)))
  .reduce(mapReduce(str => str.concat('--active')));

// ClassList.of([
//  "btn__background--solarized--active",
//  "btn__text--solarized--active",
//   "btn__overlay--solarized--active"
// ]);