How to use the through2-filter.objCtor function in through2-filter

// We map a hash to multiple fileObj's because the same file
    // might live in two different locations

    if (Array.isArray(shaMap[fileObj.hash])) {
      shaMap[fileObj.hash].push(fileObj)
    } else {
      shaMap[fileObj.hash] = [fileObj]
    }

    cb(null)
  })
}

// transform stream ctor that filters folder-walker results for only files
exports.fileFilterCtor = objFilterCtor(fileObj => {
  return fileObj.type === 'file'
})

exports.fnFilterCtor = objFilterCtor(fileObj => {
  // filter additional files out of our fn pipeline
  return fileObj.type === 'file' && !!fileObj.runtime
})

// Zip a file into a temporary directory
function zipFunction(item, tmpDir, cb) {
  const zipPath = path.join(tmpDir, item.normalizedPath + '.zip')
  const output = fs.createWriteStream(zipPath)
  const archive = archiver('zip')

  archive.file(item.filepath, { name: item.basename })
  archive.finalize()

module.exports = makeTrackDict

function makeTrackDict (paths, cb) {
  var newTrackDict = {}
  var dest = concatTrackDict(newTrackDict)
  pump(walker(paths), FileFilter(), dest, handleEos)
  // Return dest so we can destroy it
  return dest

  function handleEos (err) {
    if (err) return cb(err)
    log.info('')
    cb(null, newTrackDict)
  }
}
var FileFilter = filter.objCtor(isValidFile)

function isValidFile (data, enc, cb) {
  if (data.type !== 'file') return false
  var ext = path.extname(data.basename).substring(1)
  return validExtensions.includes(ext)
}

function concatTrackDict (obj) {
  function writeTrackDict (data, enc, cb) {
    log.info(`Scanning ${data.filepath}`)
    parseMetadata(data, handleMeta)

    function handleMeta (err, meta) {
      if (err) throw err
      obj[meta.filepath] = meta
      cb(null)

if (Array.isArray(shaMap[fileObj.hash])) {
      shaMap[fileObj.hash].push(fileObj)
    } else {
      shaMap[fileObj.hash] = [fileObj]
    }

    cb(null)
  })
}

// transform stream ctor that filters folder-walker results for only files
exports.fileFilterCtor = objFilterCtor(fileObj => {
  return fileObj.type === 'file'
})

exports.fnFilterCtor = objFilterCtor(fileObj => {
  // filter additional files out of our fn pipeline
  return fileObj.type === 'file' && !!fileObj.runtime
})

// Zip a file into a temporary directory
function zipFunction(item, tmpDir, cb) {
  const zipPath = path.join(tmpDir, item.normalizedPath + '.zip')
  const output = fs.createWriteStream(zipPath)
  const archive = archiver('zip')

  archive.file(item.filepath, { name: item.basename })
  archive.finalize()

  pump(archive, output, err => {
    if (err) return cb(err)

if (Array.isArray(shaMap[fileObj.hash])) {
      shaMap[fileObj.hash].push(fileObj)
    } else {
      shaMap[fileObj.hash] = [fileObj]
    }
    statusCb({
      type: 'hashing',
      msg: `Hashing ${fileObj.relname}`,
      phase: 'progress'
    })
    cb(null)
  })
}

// transform stream ctor that filters folder-walker results for only files
exports.fileFilterCtor = objFilterCtor(fileObj => {
  return fileObj.type === 'file'
})