collectJSON.js

const fs = require('fs').promises;
const path = require('path');
const ls = dir => fs.readdir(dir);

async function walk(dir) {
  const filesList = await ls(dir);
  const files = await Promise.all(filesList.map(async file => {
    const filePath = path.join(dir, file);
    const stats = await fs.stat(filePath);
    if (stats.isDirectory()) return walk(filePath);
    else if (stats.isFile()) return filePath;
  }));
  return files.reduce((all, folderContents) => all.concat(folderContents), []);
}

async function collectJSON(dir, fileName) {
  const fileList = await walk(dir);
  const targetFiles = fileList.filter(name => path.basename(name) === fileName);
  const jsonFiles = await Promise.all(targetFiles.map(path => fs.readFile(path, 'utf8')));
  return jsonFiles.map(string => JSON.parse(string)).reduce((acc, json) => (Object.assign(acc, json)));
}