How to use

flatten

function

in

Array

folders
  .filter(item => {
    const ret = fs.statSync(item).isDirectory();
    if (!ret)
      log("warn", `Ignoring argument "${item}" because it is not a directory`);
    return ret;
  })
  .map(path => ({root: path, files: walk(path)}))
  .map(({root, files}) => files.map(file => root + "/" + file).concat(root))
  .flatten()
  .filter(item => fs.statSync(item).isDirectory())

folders
    .filter(item => {
      if (!fs.existsSync(item + "/urls.json")) {
        log("verb", `URL collection: discarding ${item} because it doesn't contain urls.json`);
        return false;
      }
      log("debug", `URL collection: folder ${item} is valid.`);
      return true;
    })
    .map(item => JSON.parse(fs.readFileSync(item + "/urls.json")))
    .flatten()
    .uniqueStrings()