Subscribing to Events

Websockets provide a pub/sub interface where you can listen for certain events. Instead of pinging a typical HTTP endpoint at an interval to get frequent updates, you can instead receive those updates only when they happen.

Solana's web3 Connection under the hood generates a websocket endpoint and registers a websocket client when you create a new Connection instance (see source code here).

The Connection class exposes pub/sub methods - they all start with on, like event emitters. When you call these listener methods, it registers a new subscription to the websocket client of that Connection instance. The example pub/sub method we use below is onAccountChange. The callback will provide the updated state data through arguments (see AccountChangeCallback as an example).

import { clusterApiUrl, Connection, Keypair } from "@solana/web3.js";
 
(async () => {
  // Establish new connect to devnet - websocket client connected to devnet will also be registered here
  const connection = new Connection(clusterApiUrl("devnet"), "confirmed");
 
  // Create a test wallet to listen to
  const wallet = Keypair.generate();
 
  // Register a callback to listen to the wallet (ws subscription)
  connection.onAccountChange(
    wallet.publicKey(),
    (updatedAccountInfo, context) =>
      console.log("Updated account info: ", updatedAccountInfo),
    "confirmed",
  );
})();