Express.js Response

Posted in Express Tutorial

Updated on Feb 12, 2024

By Mari Selvan

👁️ 49 - Views

⏳ 4 mins

💬 1 Comment

Photo Credit to CodeToFun

🙋 Introduction

In the realm of web development with Express.js, understanding how to craft and manage responses is essential.

The res object, short for "response," is at the core of shaping what your server sends back to clients.

This page serves as a comprehensive guide to the res object, exploring its methods, capabilities, and best practices.

🧐 What is the Response Object?

In Express.js, the res object represents the HTTP response that an Express app sends when it receives an HTTP request. It provides a set of methods and properties to manipulate and control the content, headers, and status codes of the response.

🏁 Initializing the res Object

Unlike the app object, the res object is not explicitly created; it is automatically available in the callback functions handling routes or middleware. As a developer, you interact with it to construct and send the desired response.

🧠 Anatomy of the res Object

Sending Basic Responses:

The res.send() method is a versatile tool for sending responses in various formats, such as HTML, plain text, JSON, or even status codes.
sending-basic-responses.js
Copied
```
app.get('/hello', (req, res) => {
  res.send('Hello, Express!');
});

app.get('/json', (req, res) => {
  res.send({ message: 'Express is awesome!' });
});
```
Sending JSON Responses:

The res.json() method specifically formats and sends JSON responses, setting the appropriate headers automatically.
sending-json-responses.js
Copied
```
app.get('/api/data', (req, res) => {
  const data = { name: 'John Doe', age: 25, occupation: 'Developer' };
  res.json(data);
});
```
Setting Status Codes:

The res.status() method allows you to set the HTTP status code for the response, indicating success, failure, or redirection.
setting-status-codes.js
Copied
```
app.get('/not-found', (req, res) => {
  res.status(404).send('Not Found');
});
```

🔑 Key Methods and Functions

Manipulating Response Headers:

Customizing response headers is a common requirement. The res.setHeader() method allows you to set custom headers for the response.
manipulating-response-headers.js
Copied
```
app.get('/custom-headers', (req, res) => {
  res.setHeader('X-Custom-Header', 'Hello, Custom Header!');
  res.send('Check the headers of this response.');
});
```
Error Handling in Responses:

Effectively handling errors is crucial for a seamless user experience. Utilize the res.status() method in conjunction with appropriate HTTP status codes to communicate errors gracefully.
error-handling-in-responses.js
Copied
```
app.get('/error', (req, res) => {
  // Simulate an error
  const error = new Error('Something went wrong!');
  res.status(500).send(error.message);
});
```

🚀 Advanced Features

Streaming Responses:

The res.write() method allows you to stream responses, making it efficient to handle large datasets and deliver content progressively to clients.

streaming-responses.html

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app.get('/stream-data', (req, res) => {
  res.write('This ');
  setTimeout(() => res.write('is '), 1000);
  setTimeout(() => res.write('streamed '), 2000);
  setTimeout(() => res.end('data.'), 3000);
});

Redirecting Requests:

The res.redirect() method simplifies the process of redirecting clients to a different URL.
redirecting-requests.html
Copied
```
app.get('/old-url', (req, res) => {
  res.redirect('/new-url');
});
```

📝 Example

Let's combine some of the discussed concepts in a simple example:

example.js

Copied

app.get('/example', (req, res) => {
  // Sending a JSON response with a custom status code and header
  res.status(200).setHeader('X-Custom-Header', 'Example Header').json({ message: 'Express.js example' });
});

This example showcases setting the status code, custom header, and sending a JSON response.

🎉 Conclusion

Mastering the res object is fundamental to controlling server responses in Express.js. This overview has explored its various methods and functions, empowering you to shape and deliver responses efficiently.