code: function directory_path () {
        pending++
        readdir(entry, (err, children) => {
          if (err) return done(err)
  
          // Push children into pipeline, order is not important
          for (var i = children.length; i--;) {
            if (path !== null && base !== null) {
              files.push({ base, path: join(path, children[i]) })
            } else if (path !== null) {
              files.push({ base: null, path: join(path, children[i]) })
            } else {
              files.push({ base, path: children[i] })
            }
          }
  
          // Filter directory out of pipeline after adding children files
          pending--
          done(null, null)
        })
      }
docs: If path is directory, read their children and push more onto `paths` This is the recursive operation that creates more file in the pipeline