WebSocket protocol concept in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the main advantage of WebSocket over HTTP?

WebSocket is often chosen over HTTP for certain applications. What is the main advantage of using WebSocket compared to HTTP?

A WebSocket requires no handshake, so it connects instantly without delay.

B WebSocket uses less bandwidth because it compresses all messages automatically.

C WebSocket allows full-duplex communication, enabling real-time two-way data exchange.

D WebSocket is stateless, so it does not keep any connection open between client and server.

💡 Hint

Think about how data flows between client and server in real-time apps like chat.

WebSocket enables full-duplex communication, meaning both client and server can send messages independently at any time. HTTP is request-response only.

❓ component_behavior

intermediate

What happens when a WebSocket client sends a message?

In a Node.js WebSocket server, what happens immediately after a client sends a message?

Node.js

const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });
wss.on('connection', ws => {
  ws.on('message', message => {
    // What happens here?
  });
});

A The server receives the message event and can process or respond to the client immediately.

B The server queues the message and waits for the client to send a close signal before processing.

C The server ignores the message unless the client sends a ping frame first.

D The server automatically broadcasts the message to all connected clients without code.

💡 Hint

Consider the event listeners set up on the server side.

When a client sends a message, the server's 'message' event handler runs immediately, allowing the server to handle or reply to the message.

📝 Syntax

advanced

Identify the correct way to send a message to a WebSocket client in Node.js

Which of the following code snippets correctly sends a text message 'Hello' to a connected WebSocket client?

Node.js

const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });
wss.on('connection', ws => {
  // send message here
});

A ws.send('Hello');

B ws.sendMessage('Hello');

C ws.emit('send', 'Hello');

D ws.write('Hello');

💡 Hint

Check the official WebSocket API method for sending data.

The correct method to send data to a WebSocket client is send(). Other methods do not exist or do not send messages.

🔧 Debug

advanced

Why does this WebSocket server code fail to respond to clients?

Consider this Node.js WebSocket server code. Why does it never send a response back to clients?

Node.js

const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });
wss.on('connection', ws => {
  ws.on('message', message => {
    ws.sendMessage('Received: ' + message);
  });
});

A The server needs to wait for a 'ready' event before sending messages.

B The method <code>sendMessage</code> does not exist; it should be <code>send</code>.

C The server must use <code>ws.emit('message', ...)</code> to send data.

D The server must call <code>ws.connect()</code> before sending messages.

💡 Hint

Check the WebSocket API method names carefully.

The WebSocket client object has a send() method, not sendMessage(). Using a wrong method causes no message to be sent.

❓ state_output

expert

What is the final value of 'count' after this WebSocket server handles 3 client messages?

Given the following Node.js WebSocket server code, what is the value of count after three messages are received from any clients?

Node.js

const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });
let count = 0;
wss.on('connection', ws => {
  ws.on('message', message => {
    count += 1;
    ws.send(`Message number ${count}`);
  });
});

A Depends on how many clients are connected

B 1

C 0

D 3

💡 Hint

Count increases each time any client sends a message.

The variable count is incremented every time any client sends a message. After three messages total, count is 3.