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An example application to demonstrate file uploads and downloads for LoopBack 4


This application exposes POST /files endpoint that accepts multipart/form-data based file uploads. The uploaded files can be listed using GET /files and individual files can be downloaded using GET /files/<filename>.

Key artifacts

  • FileUploadController

    • Expose POST /files endpoint to allow file uploads
  • FileUploadService - an Express middleware from multer

    • A service provider that returns a configured multer request handler

      The file upload is configured with multer options in src/application.ts as follows:

      // Configure file upload with multer options
      const multerOptions: multer.Options = {
        storage: multer.diskStorage({
          // Upload files to `.sandbox`
          destination: path.join(__dirname, '../.sandbox'),
          // Use the original file name as is
          filename: (req, file, cb) => {
            cb(null, file.originalname);
  • FileDownloadController

    • Expose GET /files endpoint to list uploaded files
    • Expose GET /files/{filename} endpoint to download a file


Start the app:

npm start

The application will start on port 3000. Open http://localhost:3000 in your browser. You can try to upload a few files using the web UI or API explorer.


By default, the uploaded files will be stored in .sandbox folder under the application root directory. The directory can be configured via fileStorageDirectory of application config.



Run npm test from the root folder.


See all contributors.