JavaScript: Map, filter, reduce

In the JS: Functions course we went through three main higher-order functions for handling collections: map, filter and reduce. You can use them to solve almost any task.

solution.js

In this challenge, you will have to write your own implementation of these functions for file trees.

map takes a handler function and a tree, and returns a mapped tree.

filter takes a predicate and a tree, and returns a filtered tree by predicate.

In addition to the main parameters (the handler function and the tree), reduce also takes the initial value of the accumulator.

All functions must be exported.

Examples

import { mkdir, mkfile, getName, isDirectory } from '@hexlet/immutable-fs-trees';

const tree = mkdir('/', [
  mkdir('eTc', [
    mkfile('config.json')
  ]),
]);

Making the names of all directories and files uppercase:

map(n => ({ ...n, name: getName(n).toUpperCase() }), tree);
// {
//   name: '/',
//   type: 'directory',
//   meta: {},
//   children: [
//     {
//       name: 'ETC',
//       type: 'directory',
//       meta: {},
//       children: [{ name: 'CONFIG.JSON', type: 'file', meta: {} }],
//     },
//   ],
// }

Filtering directories:

filter((n) => isDirectory(n), tree);
// {
//   name: '/',
//   type: 'directory',
//   meta: {},
//   children: [
//     {
//       name: 'etc',
//       type: 'directory',
//       meta: {},
//       children: [],
//     },
//   ],
// }

Counting tree nodes:

reduce((acc, n) => acc + 1, tree, 0); // 3