Broadcast
- Node.js course
- Advanced
- Lesson 41/83
- 5 min
Learn to broadcast to all clients.
What is broadcast?
Broadcast means sending a message to all connected clients. In a chat app, when a user types a message the server relays it to everyone; that is a broadcast.
In the ws module you broadcast with wss.clients. wss.clients is a Set that holds all connected clients. You send to everyone with wss.clients.forEach((client) => { client.send(msg); }). Some clients may be closed; you send only to open ones by checking client.readyState === 1.
The broadcast pattern
The typical broadcast pattern: a message arrives from one client, the server relays it to all other clients. ws.on("message", (data) => { wss.clients.forEach((client) => { if (client !== ws && client.readyState === 1) { client.send(data); } }); }).
The client !== ws check prevents sending the message back to the sender. readyState === 1 sends only to open connections. This pattern is the foundation of chat-room logic. For more complex scenarios you need to group clients into rooms; this is easier in Socket.io.
Practice Log the client count
Create an empty Set (new Set()). Log .size.
Starter code
// create an empty Set
// log its sizeSample solution
const clients = new Set();
console.log(clients.size);Expected output
0
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Complete the property name
wss.____.forEach((client) => client.send(msg))wss.clients.forEach((client) => client.send(msg))Explanation: wss.clients is a Set of all connected clients.
2 Match each piece to its role
| Term | Meaning |
|---|---|
wss.clients |
All clients |
forEach |
Iterates each |
client.send |
Sends a message |
readyState === 1 |
Open connection |
3 Which data structure is used for broadcast?
- Set (wss.clients) Correct answer
- Number
- Array
- String
Explanation: wss.clients is a Set; you iterate with forEach.