Node.js http2.constants Property

Last Updated : 10 Aug, 2026

The http2.constants property in Node.js provides predefined constants used by the http2 module. These constants represent HTTP/2 error codes, header names, and other protocol-related values, making code more readable and easier to maintain.

  • http2.constants contains predefined values used while working with HTTP/2 in Node.js.
  • It includes constants for HTTP/2 error codes, header names, and protocol settings.
  • Using these constants eliminates the need to hardcode protocol-specific values.
  • It helps improve code readability and reduces the chances of errors.

Syntax:

http2.constants

Where:

  • http2: The built-in Node.js HTTP/2 module.
  • constants: An object containing predefined HTTP/2 constants.

Return Value: It returns an object with HTTP/2 constants.

Example 1:

JavaScript 
const http2 = require('http2');
const fs = require('fs');

// Private key and public certificate for access
const options = {
  key: fs.readFileSync('private-key.pem'),
  cert: fs.readFileSync('public-cert.pem'),
};

// Creating and initializing server
// by using http2.createServer() method
const server = http2.createServer(options);

const value =  http2.constants
    .NGHTTP2_FLOW_CONTROL_ERROR

console.log("error code : " + value)

server.on('stream', (stream, requestHeaders) => {
  stream.respond({ 
    ':status': 200, 
    'content-type': 'text/plain' 
  });

  stream.write('hello ');
  stream.end('world');
  
  // Stopping the server by
  // using the close() method
  server.close(() => {
    console.log("server closed");
  })
});

server.listen(8000);

// Creating and initializing client
// by using tls.connect() method
const client = http2.connect(
    'http://localhost:8000');

const req = client.request({ 
  ':method': 'GET', ':path': '/' });

req.on('response', (responseHeaders) => {
  console.log("status : " 
    + responseHeaders[":status"]);
});

req.on('data', (data) => {
  console.log('Received: %s ',
  data.toString().replace(/(\n)/gm,""));
});

req.on('end', () => {
  client.close(() => {
    console.log("client closed");
  })
});

Output:

error code : 3
status : 200
Received: hello
Received: world
client closed
server closed

Example 2:

JavaScript 
const http2 = require('http2');
const fs = require('fs');

// Private key and public certificate for access
const options = {
  key: fs.readFileSync('private-key.pem'),
  cert: fs.readFileSync('public-cert.pem'),
};

// Creating and initializing server
// by using http2.createServer() method
const server = http2.createServer(options);

const value =  http2.constants.NGHTTP2_NO_ERROR

console.log("error code : " + value)

server.on('stream', (stream, requestHeaders) => {
  stream.end('world');
  
  // Stopping the server
  // by using the close() method
  server.close(() => {
    console.log("server closed");
  })
});

server.listen(8000);

// Creating and initializing client
// by using tls.connect() method
const client = http2.connect(
    'http://localhost:8000');

const req = client.request({ 
  ':method': 'GET', ':path': '/' });

req.on('data', (data) => {
  console.log('Received: %s ',
  data.toString().replace(/(\n)/gm,""));
});

req.on('end', () => {
  client.close(() => {
    console.log("client closed");
  })
});

Output:

error code : 0
Received: world
client closed
server closed

Use Cases of http2.constants Property

  • It is used to access predefined HTTP/2 constants.
  • It is used to handle HTTP/2 error codes.
  • It is used to work with standard HTTP/2 header names.
  • It helps avoid hardcoded protocol values.

Reference: https://nodejs.org/dist/latest-v12.x/docs/api/http2.html#http2_http2_constants

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