Using Middleware and Enhancing APIs

Topic Outline (30-min)

1. Middleware Essentials:

   • Role and Execution Flow:

     • Middleware functions process requests before they reach the final route handler.

     • Middleware can modify req and res objects or terminate the request-response cycle.

   • Built-in vs. Custom Middleware:

     • Built-in middleware includes express.json() for parsing JSON.

     • Custom middleware can be created for logging, authentication, etc.

     javascript코드 복사app.use((req, res, next) => {
         console.log(`${req.method} ${req.url}`);
         next();
     });

2. Static File Serving:

   • Use middleware to serve static files like HTML, CSS, and images.

   javascript코드 복사app.use(express.static('public'));

   • Place files in a folder named public:

     • /public/home.html

     • /public/contact.html

3. Input Validation:

   • Validate request payloads using express-validator:

     javascript코드 복사const { check, validationResult } = require('express-validator');
     
     app.post('/tasks', [
         check('title').isString().notEmpty(),
         check('completed').isBoolean()
     ], (req, res) => {
         const errors = validationResult(req);
         if (!errors.isEmpty()) {
             return res.status(400).json({ errors: errors.array() });
         }
         res.send('Task is valid');
     });