Build a Real-Time Chat Application

Learn how to build a real-time chat application using GUN. This tutorial covers everything from basic messaging to advanced features like timestamps and user management.

What You’ll Build

Real-time message synchronization
User nicknames and identity
Message timestamps
Automatic scrolling
Multi-user support
Offline-first with automatic sync

Quick Start: Minimal Chat

Here’s the simplest possible chat application in just 21 lines:

<!DOCTYPE html>
<ul id='list'></ul>
<form id='form'>
  <input id='who' placeholder='name'>
  <input id='what' placeholder='say'>
  <input type='submit' value='send'>
</form>
<script src="https://cdn.jsdelivr.net/npm/gun/gun.js"></script>
<script>
gun = GUN();
chat = gun.get("chat" + location.hash);
view = document;

form.onsubmit = (eve) => {
  chat.set(who.value + ': ' + what.value);
  eve.preventDefault();
  what.value = "";
}

chat.map().on(function show(data, id){
  (view.line = view.getElementById(id) || view.createElement("li")).id = id;
  list.appendChild(view.line).innerText = data;
  window.scroll(0, list.offsetHeight);
});
</script>

How It Works

Initialize GUN: gun = GUN() creates a new GUN instance
Get Chat Room: chat = gun.get("chat" + location.hash) creates/joins a room based on URL hash
Send Messages: chat.set() adds messages to the set
Receive Messages: chat.map().on() listens for all messages in real-time

Try It Out

Save the code as chat.html
Open it in multiple browser windows
Add #room1 to the URL to join different rooms
Type messages and see them sync instantly!

Full-Featured Chat App

Here’s a more complete example with better UX:

<!DOCTYPE html>
<html>
<head>
  <title>GUN Chat</title>
  <style>
    body {
      font-family: system-ui, -apple-system, sans-serif;
      max-width: 800px;
      margin: 0 auto;
      padding: 20px;
    }
    
    .chat-messages {
      border: 1px solid #ddd;
      border-radius: 8px;
      padding: 20px;
      height: 400px;
      overflow-y: auto;
      background: #f9f9f9;
      margin-bottom: 20px;
    }
    
    .message {
      margin-bottom: 15px;
      padding: 10px;
      background: white;
      border-radius: 5px;
      box-shadow: 0 1px 3px rgba(0,0,0,0.1);
    }
    
    .message-header {
      display: flex;
      justify-content: space-between;
      margin-bottom: 5px;
    }
    
    .message-author {
      font-weight: bold;
      color: #0066cc;
    }
    
    .message-time {
      color: #666;
      font-size: 0.85em;
    }
    
    .chat-form {
      display: flex;
      gap: 10px;
    }
    
    input {
      padding: 10px;
      border: 1px solid #ddd;
      border-radius: 5px;
      font-size: 16px;
    }
    
    #name-input {
      flex: 1;
    }
    
    #message-input {
      flex: 3;
    }
    
    button {
      padding: 10px 20px;
      background: #0066cc;
      color: white;
      border: none;
      border-radius: 5px;
      cursor: pointer;
      font-size: 16px;
    }
    
    button:hover {
      background: #0052a3;
    }
  </style>
</head>
<body>
  <h1>GUN Chat</h1>
  <div class="chat-messages" id="messages"></div>
  
  <form class="chat-form" id="chat-form">
    <input id="name-input" placeholder="Your name" required>
    <input id="message-input" placeholder="Type a message..." required>
    <button type="submit">Send</button>
  </form>

  <script src="https://cdn.jsdelivr.net/npm/gun/gun.js"></script>
  <script>
    // Initialize GUN
    const gun = GUN([
      'http://localhost:8765/gun',
      'https://gun-manhattan.herokuapp.com/gun'
    ]);
    
    // Get chat reference
    const chat = gun.get('chat/' + (location.hash.slice(1) || 'lobby'));
    
    // Get DOM elements
    const form = document.getElementById('chat-form');
    const nameInput = document.getElementById('name-input');
    const messageInput = document.getElementById('message-input');
    const messagesDiv = document.getElementById('messages');
    
    // Load saved username
    const savedName = localStorage.getItem('chatName');
    if (savedName) {
      nameInput.value = savedName;
    }
    
    // Send message
    form.addEventListener('submit', (e) => {
      e.preventDefault();
      
      const username = nameInput.value.trim();
      const message = messageInput.value.trim();
      
      if (!username || !message) return;
      
      // Save username
      localStorage.setItem('chatName', username);
      
      // Create message object
      const msg = {
        who: username,
        what: message,
        when: Gun.state() // GUN's vector clock timestamp
      };
      
      // Add to chat
      chat.set(msg);
      
      // Clear input
      messageInput.value = '';
      messageInput.focus();
    });
    
    // Receive messages
    const messages = {};
    
    chat.map().once((msg, id) => {
      if (!msg || !msg.who || !msg.what) return;
      
      // Store message
      messages[id] = msg;
      
      // Render all messages sorted by timestamp
      renderMessages();
    });
    
    function renderMessages() {
      // Sort messages by timestamp
      const sorted = Object.entries(messages)
        .sort(([, a], [, b]) => (a.when || 0) - (b.when || 0));
      
      // Clear container
      messagesDiv.innerHTML = '';
      
      // Render each message
      sorted.forEach(([id, msg]) => {
        const div = document.createElement('div');
        div.className = 'message';
        div.id = id;
        
        const time = new Date(msg.when);
        const timeStr = time.toLocaleTimeString();
        
        div.innerHTML = `
          <div class="message-header">
            <span class="message-author">${escapeHtml(msg.who)}</span>
            <span class="message-time">${timeStr}</span>
          </div>
          <div class="message-content">${escapeHtml(msg.what)}</div>
        `;
        
        messagesDiv.appendChild(div);
      });
      
      // Auto-scroll to bottom
      messagesDiv.scrollTop = messagesDiv.scrollHeight;
    }
    
    // Escape HTML to prevent XSS
    function escapeHtml(text) {
      const div = document.createElement('div');
      div.textContent = text;
      return div.innerHTML;
    }
    
    // Focus message input on load
    messageInput.focus();
  </script>
</body>
</html>

React Chat Component

Here’s a production-ready React chat component:

import React, { Component } from 'react';
import Gun from 'gun/gun';

const formatMsgs = msgs => Object.keys(msgs)
  .map(key => ({ key, ...msgs[key] }))
  .filter(m => Boolean(m.when) && m.key !== '_')
  .sort((a, b) => a.when - b.when)
  .map(m => ((m.whenFmt = new Date(m.when).toLocaleString()), m));

export default class Chat extends Component {
  constructor({ gun }) {
    super();
    this.gun = gun.get('chat');
    this.state = {
      newMsg: '',
      name: (document.cookie.match(/alias\=(.*?)(\&|$|\;)/i) || [])[1] || '',
      msgs: {},
    };
  }

  componentWillMount() {
    const tmpState = {};
    this.gun.map().val((msg, key) => {
      tmpState[key] = msg;
      this.setState({ msgs: Object.assign({}, this.state.msgs, tmpState) });
    });
  }

  send = e => {
    e.preventDefault();
    const who = this.state.name || 'user' + Gun.text.random(6);
    this.setState({ name: who });
    document.cookie = ('alias=' + who);
    const when = Gun.time.is();
    const key = `${when}_${Gun.text.random(4)}`;
    this.gun.path(key).put({
      who,
      when,
      what: this.state.newMsg,
    });
    this.setState({ newMsg: '' });
  }

  render() {
    const msgs = formatMsgs(this.state.msgs);
    return (
      <div className="chat-container">
        <ul className="chat-messages">
          {msgs.map(msg =>
            <li key={msg.key}>
              <b>{msg.who}:</b> {msg.what}
              <span className="time">{msg.whenFmt}</span>
            </li>
          )}
        </ul>
        <form onSubmit={this.send}>
          <input 
            value={this.state.name} 
            className="name-input" 
            placeholder="Your name"
            onChange={e => this.setState({ name: e.target.value })} 
          />
          <input 
            value={this.state.newMsg} 
            className="message-input" 
            placeholder="Type a message..."
            onChange={e => this.setState({ newMsg: e.target.value })} 
          />
          <button onClick={this.send}>Send</button>
        </form>
      </div>
    );
  }
}

// Usage:
// const gun = Gun();
// <Chat gun={gun} />

Key Concepts

Using Sets for Messages

// Add to set (no duplicates by ID)
chat.set({ text: 'Hello' });

// Listen to all items in set
chat.map().on(message => {
  console.log(message);
});

Message Timestamps

// GUN's vector clock timestamp
const timestamp = Gun.state();

// JavaScript timestamp
const jsTime = Date.now();

// Use for sorting
const when = Gun.state();
messages.sort((a, b) => a.when - b.when);

Room/Channel Support

// Use URL hash for rooms
const room = location.hash.slice(1) || 'lobby';
const chat = gun.get('chat/' + room);

// Or user input
const room = prompt('Enter room name');
const chat = gun.get('chat/' + room);

Preventing XSS Attacks

// Always escape user content
function escapeHtml(text) {
  const div = document.createElement('div');
  div.textContent = text;
  return div.innerHTML;
}

// Use textContent instead of innerHTML
element.textContent = userMessage;

Advanced Features

Private Messages

See User Authentication for encrypted private messaging.

Message Deletion

// "Delete" by setting to null
chat.get(messageId).put(null);

// Filter out null messages
chat.map().on((msg, id) => {
  if (msg === null) {
    // Remove from UI
    document.getElementById(id)?.remove();
  }
});

Typing Indicators

// Ephemeral data (not persisted)
const presence = gun.get('presence/' + room);

messageInput.addEventListener('input', () => {
  presence.get(username).put({
    typing: true,
    lastSeen: Date.now()
  });
});

// Clear after delay
let typingTimeout;
messageInput.addEventListener('input', () => {
  clearTimeout(typingTimeout);
  typingTimeout = setTimeout(() => {
    presence.get(username).put({ typing: false });
  }, 1000);
});

Message Reactions

// Add reaction to message
function addReaction(messageId, emoji) {
  chat.get(messageId).get('reactions').get(emoji).put({
    count: 1,
    users: [currentUser]
  });
}

// Listen for reactions
chat.get(messageId).get('reactions').map().on((reaction, emoji) => {
  console.log(`${emoji}: ${reaction.count}`);
});

Next Steps

User Authentication

Add user login and private messaging

Todo App

Learn CRUD operations

P2P Networking

Understand mesh networking

API Reference

Explore the full API

Examples

Build a Chat Application

Build a Real-Time Chat Application

What You’ll Build

Quick Start: Minimal Chat

How It Works

Try It Out

Full-Featured Chat App

React Chat Component

Key Concepts

Using Sets for Messages

Message Timestamps

Room/Channel Support

Preventing XSS Attacks

Advanced Features

Private Messages

Message Deletion

Typing Indicators

Message Reactions

Next Steps

User Authentication

Todo App

P2P Networking

API Reference

Examples

​Build a Real-Time Chat Application

​What You’ll Build

​Quick Start: Minimal Chat

​How It Works

​Try It Out

​Full-Featured Chat App

​React Chat Component

​Key Concepts

​Using Sets for Messages

​Message Timestamps

​Room/Channel Support

​Preventing XSS Attacks

​Advanced Features

​Private Messages

​Message Deletion

​Typing Indicators

​Message Reactions

​Next Steps

User Authentication

Todo App

P2P Networking

API Reference

Build a Real-Time Chat Application

What You’ll Build

Quick Start: Minimal Chat

How It Works

Try It Out

Full-Featured Chat App

React Chat Component

Key Concepts

Using Sets for Messages

Message Timestamps

Room/Channel Support

Preventing XSS Attacks

Advanced Features

Private Messages

Message Deletion

Typing Indicators

Message Reactions

Next Steps