File Uploads (Multer)

File Uploads with Multer

Handling file uploads in Node.js requires parsing multipart/form-data. The most popular middleware for this is Multer.

1. Installation

npm install multer

2. Basic Setup

Multer adds a file or files object to the request object.

const express = require('express');
const multer  = require('multer');
const upload = multer({ dest: 'uploads/' });

const app = express();

app.post('/profile', upload.single('avatar'), function (req, res, next) {
  // req.file is the `avatar` file
  // req.body will hold the text fields, if there were any
  console.log(req.file);
  res.send('File uploaded!');
});

3. Custom Storage Configuration

To control the filename and destination more precisely, use diskStorage.

const storage = multer.diskStorage({
  destination: function (req, file, cb) {
    cb(null, '/tmp/my-uploads');
  },
  filename: function (req, file, cb) {
    const uniqueSuffix = Date.now() + '-' + Math.round(Math.random() * 1E9);
    cb(null, file.fieldname + '-' + uniqueSuffix);
  }
});

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

4. File Filters and Limits

Always validate file types and sizes to avoid security risks.

const upload = multer({
  storage: storage,
  limits: { fileSize: 1024 * 1024 * 5 }, // 5MB limit
  fileFilter: (req, file, cb) => {
    if (file.mimetype === 'image/png' || file.mimetype === 'image/jpeg') {
      cb(null, true);
    } else {
      cb(new Error('Only images allowed!'), false);
    }
  }
});

[!CAUTION] Never use dest and storage together. Also, ensure the upload directory exists before starting the server.