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Express.js Response Object

The response object in Express.js is used to send the HTTP response back to the client after processing the request. It contains methods and properties that help in setting the status, headers, and body of the response.

 

Key Features of the Response Object

  • Send Response Data: Allows you to send content such as HTML, JSON, or plain text back to the client.
  • Set Response Headers: Provides methods to set custom headers for the response.
  • Set Status Code: Allows you to set the HTTP status code for the response.
  • Redirects: You can issue a redirect to another URL or route.
  • Handle Content Type: Set the type of the response content (e.g., JSON, HTML).

 

Components of the Response Object

res.send()
The send() method is used to send a response. It can send various types of data, including strings, objects, arrays, and buffers.

Example:

app.get('/send-text', (req, res) => {
    res.send('Hello, world!');
});

res.json()
The json() method is used to send a JSON response. It automatically sets the Content-Type header to application/json.

Example:

app.get('/send-json', (req, res) => {
    res.json({ message: 'Hello, world!' });
});

res.status()
The status() method sets the HTTP status code of the response. This is important for indicating the outcome of the request (e.g., 200 for success, 404 for not found).

Example:

app.get('/not-found', (req, res) => {
    res.status(404).send('Page not found');
});

res.redirect()
The redirect() method is used to send a redirect response to the client, redirecting them to another URL.

Example:

app.get('/old-page', (req, res) => {
    res.redirect('/new-page');
});

res.set()
The set() method is used to set HTTP headers for the response. You can set multiple headers by passing key-value pairs.

Example:

app.get('/set-header', (req, res) => {
    res.set('X-Custom-Header', 'Value');
    res.send('Header set');
});

res.cookie()
The cookie() method is used to set a cookie in the response. This method automatically encodes the cookie value and appends it to the Set-Cookie header.

Example:

app.get('/set-cookie', (req, res) => {
    res.cookie('user', 'johnDoe');
    res.send('Cookie set');
});

res.sendFile()
The sendFile() method is used to send a file to the client. This is typically used to serve static files.

Example:

app.get('/download', (req, res) => {
    res.sendFile(__dirname + '/file.txt');
});

res.render()
The render() method is used to render a view template (if you are using a templating engine like EJS, Pug, or Handlebars).

Example:

app.get('/view', (req, res) => {
    res.render('index', { title: 'My Page' });
});

 

Example Code

const express = require('express');
const app = express();

// Send text response
app.get('/send-text', (req, res) => {
    res.send('Hello, world!');
});

// Send JSON response
app.get('/send-json', (req, res) => {
    res.json({ message: 'Hello, world!' });
});

// Set status code and send text
app.get('/not-found', (req, res) => {
    res.status(404).send('Page not found');
});

// Redirect to a new page
app.get('/old-page', (req, res) => {
    res.redirect('/new-page');
});

// Set custom header
app.get('/set-header', (req, res) => {
    res.set('X-Custom-Header', 'Value');
    res.send('Header set');
});

// Set a cookie
app.get('/set-cookie', (req, res) => {
    res.cookie('user', 'johnDoe');
    res.send('Cookie set');
});

// Send a file
app.get('/download', (req, res) => {
    res.sendFile(__dirname + '/file.txt');
});

// Render a template
app.get('/view', (req, res) => {
    res.render('index', { title: 'My Page' });
});

// Start the server
app.listen(3000, () => {
    console.log('Server is running on port 3000');
});

 

Summary

The response object in Express.js is crucial for sending data back to the client. It provides methods to send different types of responses, set status codes, headers, cookies, and even redirect requests. Understanding these methods is essential for effectively building dynamic and responsive web applications.

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