Handling File Uploads in Node.js with Multer

File uploads are an essential feature for many web applications, enabling users to upload profile pictures, documents, and other files. In a Node.js application, handling file uploads can be efficiently managed using Multer, a middleware for Express.js.

What is Multer?

Multer is a Node.js middleware designed for handling multipart/form-data, primarily used for uploading files. It simplifies the process of receiving and processing files from users via forms.

Installing Multer

To use Multer, you need to install it via npm:

npm install multer --save

Setting Up Multer

To get started, import Multer into your Node.js project and configure it.

const express = require('express');
const multer = require('multer');
const path = require('path');

const app = express();

// Configure storage engine
const storage = multer.diskStorage({
  destination: './uploads/',
  filename: (req, file, cb) => {
    cb(null, file.fieldname + '-' + Date.now() + path.extname(file.originalname));
  }
});

const upload = multer({ storage: storage });

// File upload route
app.post('/upload', upload.single('file'), (req, res) => {
  if (!req.file) {
    return res.status(400).send('No file uploaded.');
  }
  res.send(`File uploaded successfully: ${req.file.filename}`);
});

app.listen(3000, () => console.log('Server started on port 3000'));

Understanding the Code

• multer.diskStorage: Specifies the storage destination and filename structure.
• upload.single('file'): Handles a single file upload with the field name file.
• Upload Directory: Files will be stored in the uploads/ folder.

Handling Multiple File Uploads

Multer also allows multiple file uploads:

app.post('/upload-multiple', upload.array('files', 5), (req, res) => {
  res.send(`Uploaded ${req.files.length} files successfully.`);
});

Here, up to 5 files can be uploaded at once.

Filtering Files (MIME Type Validation)

To restrict uploads to specific file types, use a filter:

const fileFilter = (req, file, cb) => {
  const allowedTypes = ['image/jpeg', 'image/png', 'image/gif'];
  if (allowedTypes.includes(file.mimetype)) {
    cb(null, true);
  } else {
    cb(new Error('Only images are allowed'), false);
  }
};

const uploadWithFilter = multer({ storage, fileFilter });

Conclusion

Multer simplifies file handling in Node.js, making it easy to store, validate, and process uploads. Whether you’re building an image upload feature or handling document submissions, Multer is a reliable and efficient solution.

Happy coding!