Understanding Middleware in Simple Terms

What is Middleware?

Let's understand it in a simple way:

You have planned to go for a bike ride in the evening with your friend.

You requested your father to allow you to go for that ride. Your father said, "Okay, you can go, but meet your mother before going for a ride."

You go to meet your mother, and she hands you over a helmet that you must have in order to go for a ride.

You then go, complete the ride with the helmet.

Understanding the Analogy

• You asking to go for a bike ride is a request sent to the server.
• Your father is the server that accepts the request and decides what to do next.
• Your mother acts as a middleware that processes the request before passing it forward.
• Your friend taking you on a ride is the controller or the function executing the main task.

Role of Middleware

Middleware adds essential information to the request before it reaches the controller. For example:

• In a Node.js application, to upload a file to a CDN, we first accept files from the frontend.
• Express.js itself doesn't handle file uploads.
• We use multer as a middleware to inject files into the request body.
• The controller can then access and process the uploaded file.

Code Example

const express = require('express');
const multer = require('multer');
const upload = multer({ dest: 'uploads/' });

const app = express();

// Middleware to handle file upload
app.post('/upload', upload.single('file'), (req, res) => {
  res.send(`File uploaded: ${req.file.filename}`);
});

app.listen(3000, () => console.log('Server running on port 3000'));

Middleware functions execute before the controller, modifying the request as needed. Hope this explanation clarifies the concept!