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Supabase Backend as a Service · Lesson

Building a Live Chat Feature

Apply realtime knowledge to create a practical live chat application, demonstrating instant message delivery.

Building a Live Chat Feature is a free Supabase Backend as a Service lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Supabase Backend as a Service learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Realtime Chat: The Foundation

Welcome to building a live chat! Instant messaging is a perfect example of where realtime capabilities shine.

Users expect their messages to appear instantly without refreshing. Supabase Realtime makes this surprisingly simple.

In this lesson, we'll connect the dots: sending messages to your database and instantly receiving new messages from others.

Designing Your Chat Messages Table

First, we need a place to store our chat messages. A simple table is all it takes!

We'll create a messages table with columns for the message text, who sent it, and when it was sent.

  • id: Primary Key, unique identifier.
  • text: The message content (type: TEXT).
  • user_id: Who sent the message (type: UUID, linked to auth.users).
  • created_at: When the message was sent (type: TIMESTAMPTZ, default to now()).

Initializing Supabase Client

To interact with Supabase from your app, you'll need to initialize the client library. This sets up the connection to your project.

Make sure you have your Supabase URL and Anon Key ready. (These are covered in earlier lessons.)

import { createClient } from '@supabase/supabase-js';

const supabaseUrl = 'YOUR_SUPABASE_URL';
const supabaseAnonKey = 'YOUR_SUPABASE_ANON_KEY';

const supabase = createClient(supabaseUrl, supabaseAnonKey);

This supabase object will be your gateway to sending and receiving messages.

Sending Messages: The Insert Operation

When a user types a message and hits send, your app needs to store that message in the database.

We'll use the Supabase client's insert() method on our messages table. This adds a new row with the message text and the sender's ID.

It's a straightforward database write operation, just like adding any other data.

Code: Sending a Chat Message

Try running this example. It simulates sending a message to your Supabase messages table.

Remember to replace placeholders with your actual Supabase URL/Key and a valid user_id (e.g., from an authenticated user).

import { createClient } from '@supabase/supabase-js';

// Mock Supabase client for demonstration purposes
// In a real app, use your actual Supabase URL and Anon Key
const supabase = {
  from: (tableName) => ({
    insert: async (data) => {
      console.log(`[DEMO] Attempting to insert into ${tableName}:`);
      console.log(JSON.stringify(data, null, 2));
      // Simulate a successful response
      return { data: data, error: null };
    }
  })
};

async function sendChatMessage(messageText, senderId) {
  const { data, error } = await supabase
    .from('messages')
    .insert([
      { text: messageText, user_id: senderId }
    ]);

  if (error) {
    console.error('Error sending message:', error.message);
  } else {
    console.log('Message sent successfully:', data);
  }
}

// --- Run the example ---
sendChatMessage("Hey there, CoddyKit!", "a1b2c3d4-e5f6-7890-1234-567890abcdef");

Receiving Messages in Realtime

Sending messages is only half the story. The magic of live chat is seeing new messages instantly!

Supabase Realtime allows you to subscribe to changes in your database. We'll listen specifically for new INSERT events on our messages table.

When a new message is inserted by any user, your app will receive a notification and can update the chat display.

Code: Subscribing to New Messages

This code sets up a listener for new messages. When a message is inserted, the callback function will run.

The payload.new object contains the full data of the newly inserted message.

import { createClient } from '@supabase/supabase-js';

// Mock Supabase client for demonstration purposes
const supabase = {
  channel: (channelName) => ({
    on: (eventType, filter, callback) => {
      console.log(`[DEMO] Subscribing to channel "${channelName}" for event "${eventType}" with filter:`, JSON.stringify(filter));
      // Simulate a message arriving after a delay
      setTimeout(() => {
        const mockPayload = {
          eventType: 'INSERT',
          schema: 'public',
          table: 'messages',
          new: { id: 2, text: 'This is a new realtime message!', user_id: 'another-user-id', created_at: new Date().toISOString() },
          old: {}
        };
        console.log("[DEMO] Simulating new message arrival...");
        callback(mockPayload);
      }, 3000); // Simulate message arriving after 3 seconds
      return {
        subscribe: (cb) => {
          console.log("[DEMO] Subscription initiated.");
          // Simulate successful subscription immediately
          cb('SUBSCRIBED');
        }
      };
    }
  })
};

// --- Run the example ---
const chatChannel = supabase.channel('messages_channel');

chatChannel
  .on('postgres_changes', { event: 'INSERT', schema: 'public', table: 'messages' }, (payload) => {
    console.log('Realtime: New message received!');
    console.log('Message content:', payload.new.text);
    console.log('From user:', payload.new.user_id);
    // In a real app, you would update your UI here to display the message
  })
  .subscribe((status) => {
    if (status === 'SUBSCRIBED') {
      console.log('Successfully subscribed to new messages!');
    } else {
      console.log('Subscription status:', status);
    }
  });

Displaying Messages in Your UI

Once you receive a new message via the realtime subscription, the next step is to display it in your chat interface.

Typically, you'll take the payload.new object, extract the text, user_id, and created_at, and then dynamically add it to your chat window.

  • Create a new chat bubble/element.
  • Populate it with the message data.
  • Append it to your chat message list.
  • Consider scrolling to the bottom automatically for the best user experience!

Adding User Context & Timestamps

A basic chat works, but a good chat shows who sent what and when.

Since our messages table has a user_id, you can fetch user profiles (e.g., username, avatar) to display alongside messages. This might involve a simple join if you're querying historical messages, or fetching user details separately for realtime messages.

The created_at timestamp automatically provided by Supabase is crucial for ordering messages and showing when they were sent.

Quick Check: Chat Flow

You're building a live chat. What are the two primary Supabase client operations you'll use to make messages appear instantly for all users?

Recap: Your Live Chat Feature

You've successfully built the core of a live chat feature!

We covered:

  • Designing a simple messages table.
  • Sending new messages by inserting data into Supabase.
  • Receiving new messages instantly using Supabase Realtime subscriptions.
  • How to integrate these messages into your app's UI.

This pattern of inserting data and subscribing to changes is fundamental for many realtime applications beyond just chat. Keep exploring!

Frequently asked questions

Is the “Building a Live Chat Feature” lesson free?

Yes — the full text of “Building a Live Chat Feature” is free to read here on the web, and the Supabase Backend as a Service course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Supabase Backend as a Service course, upgrade to CoddyKit PRO.

What will I learn in “Building a Live Chat Feature”?

Apply realtime knowledge to create a practical live chat application, demonstrating instant message delivery. You practise Supabase Backend as a Service with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Supabase Backend as a Service?

No prior experience is required. Supabase Backend as a Service on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Building a Live Chat Feature” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Supabase Backend as a Service lesson?

Yes. Every Supabase Backend as a Service lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Understanding Realtime Subscriptions
  2. Subscribing to Table Changes
  3. Building a Live Chat Feature
  4. Presence and Broadcast Channels
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