ExpressJS File Uploads (Multer)

npm install multer

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

// Configure storage
const storage = multer.diskStorage({
  destination: (req, file, cb) => {
    cb(null, 'uploads/'); // Files will be saved in 'uploads' folder
  },
  filename: (req, file, cb) => {
    // Create unique filename: timestamp + original extension
    const uniqueSuffix = Date.now() + '-' + Math.round(Math.random() * 1E9);
    cb(null, file.fieldname + '-' + uniqueSuffix + path.extname(file.originalname));
  }
});

// File filter function
const fileFilter = (req, file, cb) => {
  // Accept only images
  if (file.mimetype.startsWith('image/')) {
    cb(null, true);
  } else {
    cb(new Error('Only images are allowed!'), false);
  }
};

// Create multer instance with configuration
const upload = multer({
  storage: storage,
  limits: { fileSize: 5 * 1024 * 1024 }, // 5MB limit
  fileFilter: fileFilter
});

// Serve static files from uploads folder (so users can view uploaded images)
app.use('/uploads', express.static('uploads'));

// Single file upload route
app.post('/upload/single', upload.single('profilePic'), (req, res) => {
  try {
    // req.file contains information about the uploaded file
    console.log(req.file);
    res.json({
      success: true,
      message: 'File uploaded successfully',
      file: req.file
    });
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

  
  Upload

// Upload multiple files (max 5) with same field name
app.post('/upload/multiple', upload.array('photos', 5), (req, res) => {
  try {
    // req.files is an array of uploaded files
    console.log(req.files);
    res.json({
      success: true,
      message: `${req.files.length} files uploaded successfully`,
      files: req.files
    });
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

// Upload multiple files with different field names
app.post('/upload/fields', upload.fields([
  { name: 'avatar', maxCount: 1 },
  { name: 'gallery', maxCount: 8 }
]), (req, res) => {
  // req.files is an object with field names as keys
  console.log(req.files);
  res.json({
    success: true,
    avatar: req.files['avatar'][0],
    gallery: req.files['gallery']
  });
});

app.post('/upload/profile', upload.single('profilePic'), (req, res) => {
  // req.body contains text fields
  const { name, email, bio } = req.body;
  const profilePic = req.file;

  // Save user data and file info to database
  // ... your database logic here

  res.json({
    success: true,
    user: { name, email, bio },
    profilePic: profilePic
  });
});

const multer = require('multer');

app.post('/upload', (req, res) => {
  upload.single('file')(req, res, (err) => {
    if (err instanceof multer.MulterError) {
      // A Multer error occurred (e.g., file too large)
      return res.status(400).json({ error: err.message });
    } else if (err) {
      // An unknown error occurred
      return res.status(500).json({ error: err.message });
    }
    // Everything went fine
    res.json({ success: true, file: req.file });
  });
});

• Multer handles multipart/form-data for file uploads in Express.
• Configure storage (diskStorage) to control where and how files are saved.
• Use fileFilter to restrict file types (e.g., only images).
• Set limits to prevent large file uploads.
• Use upload.single(), upload.array(), or upload.fields() for different upload scenarios.
• Always handle Multer errors properly.
• Remember to create the uploads folder before saving files.