Node response.writeHead() Method

The `response.writeHead()` property, introduced in Node.js v1.0, is part of the ‘http‘ module. It is used to send a response header to the incoming request. The status code represents a 3-digit HTTP status code (e.g., 404), and the headers parameter contains the response headers. Optionally, a human-readable statusMessage can be provided as the second argument.

When using `response.setHeader()`, headers set with it will merge with those passed to `response.setHeader()`, where the latter takes precedence. If `response.writeHead()` is called without prior use of `response.setHeader()`, it directly writes supplied headers to the network channel, bypassing internal caching. This can affect the expected result of `response.getHeader()`. For progressive header population with future retrieval and modification, prefer using `response.setHeader()`.

In order to get a response and a proper result, we need to import ‘http’ module.

Syntax to Import:

const http = require('http');

Syntax:

response.writeHead(statusCode[, statusMessage][, headers]);

Parameters: It accepts three parameters as mentioned above and described below:

• statusCode <number>: It accepts the status codes that are of number type.
• statusMessage <string>: It accepts any string that shows the status message.
• headers <Object>: It accepts any function, array, or string.

Return Value <http.ServerResponse>: It returns a reference to the ServerResponse, so that calls can be chained.

Example 1: The below example illustrates the use of response.writeHead() property in Node.js.

Javascript

// Node.js program to demonstrate the
// response.writeHead() Method

// Importing http module
var http = require('http');

// Setting up PORT
const PORT = process.env.PORT || 3000;

// Creating http Server
var httpServer = http.createServer(
    function (request, response) {
        const body = 'hello world';

        // Calling response.writeHead method
        response.writeHead(200,
            {
                'Content-Length':
                    Buffer.byteLength(body),
                'Content-Type':
                    'text/plain'
            });

        response.end(body);
    });

// Listening to http Server
httpServer.listen(PORT,
    () => {
        console.log("Server is running at port 3000...");
    });

Step to run index.js file using the following command:

node index.js

Console Output:

Server is running at port 3000...

Example 2: The below example illustrates the use of response.writeHead() property in Node.js.

Javascript

// Node.js program to demonstrate the
// response.writeHead() Method

// Importing http module
var http = require('http');

// Setting up PORT
const PORT = process.env.PORT || 3000;

// Creating http Server
var httpServer = http.createServer(
    function (request, response) {

        // Setting up Headers
        response.setHeader('Content-Type', 'text/html');
        response.setHeader(
            'Set-Cookie',
            [
                'type=ninja',
                'language=javascript'
            ]);
        response.setHeader('X-Foo', 'bar');

        // Calling response.writeHead method
        response.writeHead(200,
            {
                'Content-Type': 'text/plain'
            });

        // Getting the set Headers
        const headers = response.getHeaders();

        // Printing those headers
        console.log(headers);

        // Prints Output on the
        // browser in response
        response.end('ok');
    });

// Listening to http Server
httpServer.listen(PORT, () => {
    console.log(
        "Server is running at port 3000...");
});

Step to run index.js file using the following command:

node index.js

Output:

Server is running at port 3000...
[Object: null prototype] {
 'content-type': 'text/plain', 
 'set-cookie': [ 'type=ninja', 'language=javascript' ], 
 'x-foo': 'bar'}

We have a complete list of Express.js Response methods, properties and events, to check those please go through this Express.js Response Complete Reference article.