README.md

Lecture 16 - [Backend 3] Understand Express Middleware

• Middleware
• Project Structure
• Project

Middleware

• What is Middleware?

  • Middleware is just a controller function. It comes from DRY (Don't repeat yourself) principle. It actually used to reuse the controller. Req -> M1 -> M2 -> M3 -> Res

    // We will never call it, express will automatically invoke for us.
    // This is middleware
    function xyz(req, res, next) {
    	next();
    }
    
    // This is controller
    function xyz(req, res, next) {
    	res.send();
    }

    The basic difference between a middleware and controller is, middleware calls next() function and a controller calls function related to response.

    // Demo Code
    const express = require('express');
    
    const app = express();
    
    app.use(express.static(__dirname + '/public'));
    
    const simpleLogger = (req, res, next) => {
    	console.log(`${req.url} - ${req.method} - ${new Date().toISOString()}`);
    	next();
    };
    
    const secondMiddleWare = (res, req, next) => {
    	console.log('I am second middleware');
    	next();
    };
    
    app.use([simpleLogger, secondMiddleWare]);
    
    app.get('/hello', (req, res, next) => {
    	res.json({ message: 'Hello' });
    });
    
    app.get('/', (req, res, next) => {
    	res.json({ message: 'Sweet Home' });
    });
    
    app.listen(8000, () => {
    	console.log('Application running on port 8000');
    });

References

• Source Code
• HTTP status code
• Class Overview

Task

• Watch the video and create the structure as shown in video. Write and article with explanation of the structure.