Understanding the Role of Request and Response Objects in Express.js

In Express.js, the request (req) and response (res) objects are essential for handling HTTP transactions between a client and a server. Here's what you should know:

Request Object (req)

• Represents the HTTP request made by the client
• Contains details such as:
  • URL parameters (req.params)
  • Query strings (req.query)
  • Headers (req.headers)
  • Request body (req.body)

Example:

app.get('/users/:id', (req, res) => {
  // Access URL parameter
  const userId = req.params.id;
  res.send(`User ID is ${userId}`);
});

Response Object (res)

• Facilitates sending a response back to the client
• Methods include:
  • res.send() for sending a response body
  • res.json() for JSON data
  • res.status() to set response status codes
  • res.redirect() to redirect clients

Example:

app.post('/login', (req, res) => {
  const { username, password } = req.body;
  if(username === 'admin') {
    res.status(200).json({ message: 'Login successful' });
  } else {
    res.status(401).send('Unauthorized');
  }
});

Summary

• req lets you read data sent by the client
• res allows you to construct and send an appropriate reply

Mastering these objects is central to building efficient Express.js servers.