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ws module

Learn WebSocket servers with the ws module.

What is the ws module?

ws is the most popular lightweight WebSocket module for Node.js. WebSocket provides a bidirectional, persistent connection between server and client; unlike HTTP it does not reconnect per request.

Install: npm install ws. WebSocket is ideal for real-time apps: chat, live notifications, games. The ws module is low-level; for higher-level features use Socket.io. But ws is lighter and has less overhead. You import it with require("ws").

WebSocket vs HTTP

HTTP is request-response based: the client asks, the server answers, the connection closes. WebSocket keeps the connection open; either side can send a message at any time.

This is critical for real-time apps. In a chat app the server can push a new message instantly; it does not wait for the client to ask. WebSocket starts with an HTTP handshake, then upgrades to the WebSocket protocol. That is why it uses the same ports (80/443).

Practice Log the type of WebSocketServer

Import the WebSocketServer class from ws. Log typeof WebSocketServer.

Starter code

index.js
// import the module, get the server class

// log its type

Sample solution

index.js
const { WebSocketServer } = require("ws");
console.log(typeof WebSocketServer);

Expected output

function

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What does the ws module provide?

  • A persistent two-way connection Correct answer
  • One-way HTTP
  • File compression
  • Network acceleration

Explanation: The ws module provides a bidirectional persistent connection.

2 Complete the module name

Question 
const { WebSocketServer } = require("____")
Answer 
const { WebSocketServer } = require("ws")

Explanation: The ws module loads as 'ws'.

3 Match each piece to its role

Term Meaning
ws WebSocket module
WebSocketServer Server class
npm install ws Installs the module
require("ws") Imports the module

All lessons in Advanced

1 Clustering

  1. cluster module
  2. cluster.fork
  3. Worker IPC
  4. cluster.isMaster
  5. Graceful reload
  6. Summary - Clustering

2 Worker threads

  1. worker_threads
  2. Worker
  3. postMessage
  4. MessageChannel
  5. SharedArrayBuffer
  6. Summary - Worker threads

3 Performance

  1. perf_hooks
  2. Event loop latency
  3. Memory usage
  4. CPU profiling
  5. Optimization
  6. Summary - Performance

4 Security

  1. Helmet
  2. CORS
  3. Rate limiting
  4. Input validation
  5. JWT
  6. Summary - Security

5 MongoDB

  1. Mongoose
  2. Schema
  3. Model
  4. Query
  5. Aggregate
  6. Summary - MongoDB

6 SQL database

  1. pg module
  2. Pool
  3. Parameterized query
  4. Transactions
  5. Sequelize
  6. Summary - SQL database

7 WebSocket

  1. ws module
  2. WebSocket server
  3. Connection
  4. Message
  5. Broadcast
  6. Summary - WebSocket

8 Realtime

  1. Socket.io
  2. io.on
  3. emit and on
  4. Rooms
  5. Namespaces
  6. Summary - Realtime

9 Microservice basics

  1. What are microservices?
  2. Service communication
  3. API gateway
  4. Service discovery
  5. Circuit breaker
  6. Summary - Microservices

10 Message queue

  1. What are message queues?
  2. Bull
  3. Producer
  4. Consumer
  5. Retry and backoff
  6. Summary - Message queue

11 Logging

  1. Winston
  2. Log levels
  3. Transports
  4. Structured logging
  5. Pino
  6. Summary - Logging

12 Configuration

  1. dotenv
  2. Environment variables
  3. Config hierarchy
  4. Validation
  5. Secrets management
  6. Summary - Configuration

13 Advanced testing

  1. Integration tests
  2. Supertest
  3. Test database
  4. Coverage
  5. E2E tests
  6. Summary - Advanced testing

14 Advanced final

  1. Project design
  2. Express + DB
  3. WebSocket
  4. Security
  5. Putting it together