eth_subscribe

Track pending transaction hashes on peaq using eth_subscribe over WebSockets. Handle incoming notifications, errors, and subscription cleanup.

Pending transactions have been submitted to the network but are not yet in a block. eth_subscribe pushes their hashes to you as they enter the transaction pool (mempool), so your application can track transactions or watch network activity without polling.

This guide subscribes to pending transactions over a WebSocket connection to a peaq node. The example creates the subscription, handles incoming hashes and errors, and cleans up the subscription and the connection on shutdown.

Prerequisites

• Node.js installed.
• A WebSocket endpoint for a peaq node (wss://quicknode1.peaq.xyz).
• The web3, dotenv, and web3-providers-ws packages.

Instructions

1. Setting Up the Environment

• Install Dependencies: Install the packages:

npm install web3 dotenv web3-providers-ws

• Set ESM Module: Add the following to your package.json to allow for ESM modules.

"type": "module",

• Configure Environment Variables: Create a .env file with the following content:

PEAQ_WS_URL=wss://quicknode1.peaq.xyz

2. How eth_subscribe works

eth_subscribe is a JSON-RPC method available over WebSocket connections. Calling web3.eth.subscribe('pendingTransactions') tells the node to push a notification for every new transaction it sees in the mempool. Each notification carries one transaction hash and arrives on the subscription’s "data" event. Network errors and dropped connections arrive on its "error" event.

3. Run the example

The script opens a WebSocket provider against PEAQ_WS_URL, subscribes to pending transactions, and registers a SIGINT handler (Ctrl+C) that unsubscribes and disconnects the provider before exiting.

JavaScript

// eth_subscribe_pendingTx.js

import dotenv from 'dotenv';
dotenv.config();

import Web3 from 'web3';
import WSProvider from 'web3-providers-ws';

const WS_URL = process.env.PEAQ_WS_URL;
const provider = new WSProvider(WS_URL);
const web3 = new Web3(provider);

let pendingSubscription;

(async () => {
  try {
    pendingSubscription = await web3.eth.subscribe('pendingTransactions');
    pendingSubscription.on("data", (txHash) => {
      console.log("Pending Transaction Hash received:");
      console.log(txHash);
    });
    pendingSubscription.on("error", (error) => {
      console.error("Error in pendingTransactions subscription:", error);
    });
  } catch (err) {
    console.error("Error subscribing to pendingTransactions:", err);
  }
})();

// Graceful shutdown
process.on('SIGINT', async () => {
  console.log("\nGracefully shutting down...");
  try {
    if (pendingSubscription) {
      await pendingSubscription.unsubscribe();
      console.log("Unsubscribed from pendingTransactions.");
    }
  } catch (err) {
    console.error("Error unsubscribing from pendingTransactions:", err);
  }
  provider.disconnect();
  process.exit();
});

console.log("Listening for pending transactions on the peaq network (eth_subscribe)...");

The terminal will output the pending transaction hash as follows: