s3Zip-express-folder.js

var s3Zip = require('s3-zip')

var listObjects = function (opts) {
  return new Promise (function (resolve, reject) {
    var keys = []
    var getKeys = function (token) {
      if (token) {
        opts.ContinuationToken = token
      } else {
        delete opts.ContinuationToken
      }
      s3.listObjectsV2(opts, function (err, data) {
        keys = keys.concat(data.Contents)
        if (data.IsTruncated) {
          getKeys(data.NextContinuationToken)
        } else {
          resolve(keys)
        }
      })
    }
    getKeys()
  })
}

var zipFiles = function (request, response) {
  listObjects({
          Bucket: bucket,
          Prefix: folder
        })
          .then(function (objects) {
            objects = objects.filter(object => object.Size > 0)
            objects = objects.map(object => object.Key)
            response.set('content-type', 'application/zip')
            response.set('content-disposition', 'attachment; filename="filename.zip"')
            s3Zip
              .archive({
                region: region,
                bucket: bucket,
                preserveFolderStructure: true
              }, '', objects) // folder is empty due to the list of objects containing it
              .pipe(response)
          })
}

app.get('/download', zipFiles)