Creating a basic HTTP server in Node.js - Performance Optimization Steps

Performance: Creating a basic HTTP server

MEDIUM IMPACT

This concept affects the initial server response time and how quickly the browser receives the first byte of content.

Serving a simple HTML page with Node.js

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  res.writeHead(200, {'Content-Type': 'text/html'});
  function writeLines(i) {
    let ok = true;
    while (i < 10000 && ok) {
      ok = res.write(`<p>Line ${i}</p>`);
      i++;
    }
    if (i < 10000) {
      res.once('drain', () => writeLines(i));
    } else {
      res.end();
    }
  }
  writeLines(0);
});

server.listen(3000);

Streaming the response in chunks avoids blocking the event loop and starts sending data earlier.

📈 Performance GainStarts sending bytes immediately, reducing time to first byte and improving LCP.

Serving a simple HTML page with Node.js

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  let html = '';
  for (let i = 0; i < 10000; i++) {
    html += '<p>Line ' + i + '</p>';
  }
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.end(html);
});

server.listen(3000);

Building a large HTML string synchronously blocks the event loop and delays sending the response.

📉 Performance CostBlocks event loop for 50-100ms depending on CPU, delaying first byte and LCP.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Synchronous large string build before response	N/A (server-side)	N/A	N/A	[X] Bad
Streaming response in chunks	N/A (server-side)	N/A	N/A	[OK] Good

Rendering Pipeline

The server sends the HTTP response which the browser receives and parses. Faster server response means the browser can start rendering sooner.

→Network

→First Byte

→HTML Parsing

→Rendering

⚠️ BottleneckServer-side blocking operations delay the first byte, slowing LCP.

Core Web Vital Affected

LCP

This concept affects the initial server response time and how quickly the browser receives the first byte of content.

Optimization Tips

1Avoid heavy synchronous processing before sending response.

2Stream response data in chunks to start sending early.

3Monitor Time to First Byte (TTFB) to gauge server response speed.

Performance Quiz - 3 Questions

What server behavior improves the Largest Contentful Paint (LCP) when creating a basic HTTP server?

A Building the entire response string before sending

B Sending the response in small chunks as soon as possible

C Delaying response until all data is ready

D Using synchronous blocking code to prepare response

DevTools: Network

How to check: Open DevTools, go to Network tab, reload page, and check the 'Time to First Byte' (TTFB) for the server response.

What to look for: Lower TTFB indicates faster server response and better LCP performance.

Practice

1. What does the http.createServer() function do in Node.js?

easy

A. It compiles JavaScript code into machine code.

B. It creates a database connection for storing data.

C. It creates a server that listens for HTTP requests and sends responses.

D. It formats JSON data for sending over the network.

Solution

1. Step 1: Understand the purpose of http.createServer()

   This function sets up a server that waits for HTTP requests from clients like browsers.

2. Step 2: Identify what the server does

   The server uses a function to handle incoming requests and send back responses, enabling communication over the web.

3. Final Answer:

   It creates a server that listens for HTTP requests and sends responses. -> Option C

4. Quick Check:

   HTTP server creation = It creates a server that listens for HTTP requests and sends responses. [OK]

Hint: Remember: createServer sets up the web server [OK]

Common Mistakes:

• Confusing server creation with database connection
• Thinking it compiles code
• Mixing up data formatting with server setup

2. Which of the following is the correct way to start a Node.js HTTP server on port 3000?

easy

A. http.listen(3000);

B. server.listen(3000);

C. server.start(3000);

D. server.run(3000);

Solution

1. Step 1: Identify the method to start the server

   The correct method to make the server listen on a port is listen().

2. Step 2: Match the method with the server object

   Calling server.listen(3000); starts the server on port 3000.

3. Final Answer:

   server.listen(3000); -> Option B

4. Quick Check:

   Start server with listen() = server.listen(3000); [OK]

Hint: Use listen() to start the server on a port [OK]

Common Mistakes:

• Using non-existent methods like start() or run()
• Calling listen() on http instead of server
• Confusing server methods with other modules

3. What will the following Node.js code output when accessed via a browser?

const http = require('http');
const server = http.createServer((req, res) => {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World');
});
server.listen(4000);

medium

A. Hello World

B. Error: server.listen is not a function

C. 404 Not Found

D. Hello

Solution

1. Step 1: Analyze the server response setup

   The server sets the HTTP status to 200 (OK) and content type to plain text, then sends 'Hello World' as the response body.

2. Step 2: Understand what the browser receives

   When accessed, the browser will display the exact string 'Hello World' from the server response.

3. Final Answer:

   Hello World -> Option A

4. Quick Check:

   Response text = Hello World [OK]

Hint: Check res.end() content for output text [OK]

Common Mistakes:

• Expecting an error due to incorrect method
• Confusing status codes with output text
• Assuming partial output without reading res.end()

4. Identify the error in this Node.js HTTP server code:

const http = require('http');
const server = http.createServer((req, res) => {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.write('Welcome');
  res.end();
});
server.listen(8080)
console.log('Server running on port 8080');

medium

A. Incorrect Content-Type header value

B. Using res.write() without res.end() causes error

C. Missing semicolon after server.listen(8080)

D. No error; code runs correctly and serves 'Welcome'

Solution

1. Step 1: Check syntax and method usage

   The code correctly calls res.write() followed by res.end(), which is valid to send response data.

2. Step 2: Verify headers and server start

   The Content-Type is valid as 'text/html', and server.listen(8080) starts the server properly. Missing semicolons are optional in JavaScript.

3. Final Answer:

   No error; code runs correctly and serves 'Welcome' -> Option D

4. Quick Check:

   Valid server code = No error; code runs correctly and serves 'Welcome' [OK]

Hint: res.write() + res.end() is valid to send response [OK]

Common Mistakes:

• Thinking missing semicolons cause errors
• Believing res.write() must be avoided
• Assuming wrong Content-Type causes failure

5. You want to create a Node.js HTTP server that responds with JSON data {"status":"ok"} and sets the correct header. Which code snippet correctly does this?

hard

A. const server = http.createServer((req, res) => {
res.writeHead(200, {'Content-Type': 'application/json'});
res.end(JSON.stringify({status: 'ok'}));
});

B. const server = http.createServer((req, res) => {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('{"status":"ok"}');
});

C. const server = http.createServer((req, res) => {
res.writeHead(404, {'Content-Type': 'application/json'});
res.end(JSON.stringify({status: 'ok'}));
});

D. const server = http.createServer((req, res) => {
res.writeHead(200);
res.end({status: 'ok'});
});

Solution

1. Step 1: Set correct Content-Type header for JSON

   The header must be 'application/json' to tell the client the response is JSON data.

2. Step 2: Send JSON string as response body

   Use JSON.stringify() to convert the object to a JSON string before sending with res.end().

3. Final Answer:

   Code snippet with application/json header and JSON.stringify() -> Option A

4. Quick Check:

   JSON header + stringified data = const server = http.createServer((req, res) => { res.writeHead(200, {'Content-Type': 'application/json'}); res.end(JSON.stringify({status: 'ok'})); }); [OK]

Hint: Use application/json header and JSON.stringify() [OK]

Common Mistakes:

• Sending object directly without stringifying
• Using wrong Content-Type header
• Sending JSON string with text/plain header
• Using 404 status instead of 200