Node.js response.getHeaderNames() Method

The response.getHeaderNames() (Added in v7.7.0) method is an inbuilt application programming interface of the ‘http‘ module which returns an array containing the unique names of the current outgoing headers. All header names are lowercase.

When headers have been set with response.setHeader(), they will be merged with any headers passed to response.writeHead(), with the headers passed to response.writeHead() given precedence.

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

Syntax:

const http = require('http');

Syntax:

response.getHeaderNames()

Parameters: This property does not accept any parameter.

Return Value: It returns the names of all the headers in string format as explained below by Example.

The below example illustrates the use of response.getHeaderNames() Method in Node.js.

Example 1: Filename: index.js

// Node.js program to demonstrate the
// response.getHeaderNames() 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(req, response) {

  // Setting up Headers
  response.setHeader('Alfa', 'Beta');
  response.setHeader('Foo', 'bar');
  response.setHeader('Set-Cookie',
           ['foo=bar', 'bar=baz']);

  const headerNames = response.getHeaderNames();
  console.log(headerNames);
  response.end("200, ok");
});

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

Output:

Output: In Console

>> Server is running at port 3000…

>> [ ‘alfa’, ‘foo’, ‘set-cookie’ ] 

Now run http://localhost:3000/ in the browser.

Output: In Browser

200, ok

Example 2: Filename: index.js

// Node.js program to demonstrate the
// response.getHeaderNames() 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(req, response) {

  // Setting up Headers
  response.setHeader('Alfa', 'Beta');
  response.setHeader('Alfa1', '');
  response.setHeader('Alfa2', 5);
  response.setHeader('Cookie-Setup',
  ['Alfa=Beta', 'Beta=Romeo']);

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

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

  // Printing headerNames
  console.log(headerNames);

  var Output = "Hello Geeksforgeeks...,"
     + " Available headerNames are:"
     + JSON.stringify(headerNames);

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

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

Run index.js file using the following command:

node index.js

Output:

Output: In Console

Server is running at port 3000…

>> [Object: null prototype] {

    alfa: ‘Beta’,

     alfa1: ”,

     alfa2: 5,

    ‘cookie-setup’: [ ‘Alfa=Beta’, ‘Beta=Romeo’ ]}

>> [ ‘alfa’, ‘alfa1’, ‘alfa2’, ‘cookie-setup’ ]

Now run http://localhost:3000/ in the browser.

Output: In Browser

Hello Geeksforgeeks…, Available headers and trailers are:{“alfa1″:””, “cookie-setup”:[“Alfa=Beta”, “Beta=Romeo”],

“content-type”:”text/plain”, “trailer”:”Content-MD5″}ok

Reference: https://nodejs.org/api/http.html#http_response_getheadernames