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.