Node.js http.ServerResponse.writableEnded Property

The http.ServerResponse.writableEnded property is a Boolean value that indicates whether the response has been ended or not. It is available on the http.ServerResponse object, which is a built-in class in Node.js that is used to handle the server-side response to an HTTP request.

Introduction

When writing server-side applications using Node.js, handling HTTP requests and sending responses is a crucial part. The http.ServerResponse object represents the writable side of an HTTP response that a server sends back to a client.

The writableEnded property comes into play during the lifecycle of an HTTP response. It helps to determine if the response has already been ended, ensuring that no further data can be written to it. This property is useful when dealing with asynchronous flow control or tracking the status of a response without relying on callback functions.

Usage and Syntax

The writableEnded property is a read-only Boolean value. It can be accessed on the http.ServerResponse object as follows:

response.writableEnded

Here, response refers to the http.ServerResponse object associated with the current HTTP request/response cycle.

Example

Consider the following example to illustrate the usage of the writableEnded property:

const http = require('http');

const server = http.createServer((request, response) => {
  response.setHeader('Content-Type', 'text/plain');
  response.write('Hello, World!');

  if (response.writableEnded) {
    console.log('Response has already been ended.');
  } else {
    response.end();
    console.log('Response has been ended.');
  }
});

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

In this example, a simple HTTP server is created using the http module. The server responds with a "Hello, World!" message. Before calling the end() method, the code checks if the response is already ended by accessing the writableEnded property. If it is true, it logs a message stating that the response has already been ended. Otherwise, it ends the response by calling the end() method and logs that the response has been ended.

Conclusion

The http.ServerResponse.writableEnded property is a convenient way to check if an HTTP response has already been ended. By using this property, you can ensure that no further data is written to the response, preventing any errors that may occur by overwriting or sending additional data. Understanding the lifecycle of an HTTP response and effectively utilizing the writableEnded property can enhance the reliability and performance of your Node.js server-side applications.