**Course Title:** Mastering Express.js: Building Scalable Web Applications and APIs **Section Title:** File Uploads and Handling Form Data **Topic:** Implementing file uploads using Multer middleware **Introduction** In this topic, we will explore how to implement file uploads using the Multer middleware in Express.js applications. Multer is a popular middleware that simplifies the process of handling multipart/form-data requests, which are used to upload files. **What is Multer?** Multer is a Node.js middleware that handles multipart/form-data requests, which are used to upload files. It provides a simple and efficient way to handle file uploads, and it is widely used in Express.js applications. **Installing Multer** To use Multer in your Express.js application, you need to install it using npm or yarn. You can install Multer using the following command: ```bash npm install multer ``` or ```bash yarn add multer ``` **Configuring Multer** To use Multer, you need to configure it to handle file uploads. You can do this by creating a Multer instance and specifying the upload directory. ```javascript const express = require('express'); const multer = require('multer'); const app = express(); const upload = multer({ dest: './uploads/', // upload directory limits: { fileSize: 1000000 }, // file size limit (1MB) fileFilter(req, file, cb) { if (!file.originalname.match(/\.(jpg|jpeg|png)$/)) { return cb(new Error('Only image files are allowed!')); } cb(null, true); }, }); app.post('/upload', upload.single('file'), (req, res) => { // req.file contains the uploaded file // req.body contains the entire request body res.send(`File uploaded successfully! File name: ${req.file.originalname}`); }); ``` In the above code, we create a Multer instance and specify the upload directory as './uploads/'. We also set a file size limit of 1MB and a file filter to only allow image files. **Handling File Uploads** To handle file uploads, you can use the `upload.single('file')` method, which expects a single file to be uploaded. The `req.file` object contains the uploaded file, and the `req.body` object contains the entire request body. **Example Use Case** Here's an example use case for implementing file uploads using Multer: ```javascript const express = require('express'); const multer = require('multer'); const app = express(); const upload = multer({ dest: './uploads/', // upload directory limits: { fileSize: 1000000 }, // file size limit (1MB) fileFilter(req, file, cb) { if (!file.originalname.match(/\.(jpg|jpeg|png)$/)) { return cb(new Error('Only image files are allowed!')); } cb(null, true); }, }); app.post('/upload', upload.single('file'), (req, res) => { // req.file contains the uploaded file // req.body contains the entire request body res.send(`File uploaded successfully! File name: ${req.file.originalname}`); }); app.get('/download', (req, res) => { const file = req.file; if (!file) { return res.status(404).send('No file found!'); } res.download(file.path, file.originalname); }); app.get('/files', (req, res) => { const files = req.files; if (!files) { return res.status(404).send('No files found!'); } res.send(files.map((file) => file.originalname)); }); ``` In the above code, we create three routes: `/upload`, `/download`, and `/files`. The `/upload` route handles file uploads using Multer, the `/download` route downloads the uploaded file, and the `/files` route returns a list of all uploaded files. **Key Concepts** * Multer is a Node.js middleware that handles multipart/form-data requests, which are used to upload files. * To use Multer, you need to install it using npm or yarn and configure it to handle file uploads. * You can use the `upload.single('file')` method to handle single file uploads. * The `req.file` object contains the uploaded file, and the `req.body` object contains the entire request body. **Practical Takeaways** * Use Multer to handle file uploads in your Express.js applications. * Configure Multer to handle file uploads by specifying the upload directory and file size limit. * Use the `upload.single('file')` method to handle single file uploads. * Use the `req.file` object to access the uploaded file and the `req.body` object to access the entire request body. **Leave a comment or ask for help if you have any questions or need further clarification on any of the concepts covered in this topic.**