Developer Fundamentals

3. Contract Whispers

Subscribe to smart contract events (e.g., VTHO Transfer) via filters.

Prerequisites

Contract Event Streams

Contracts whisper events—listen up! 👂 Use SDK for targeted streams.

In this example we are using VTHO contract address (0x0000000000000000000000000000456e65726779).

import { subscriptions } from '@vechain/sdk-network';
import WebSocket from 'ws';
// Fetch ABI: await fetch('https://raw.githubusercontent.com/vechain/b32/master/ABIs/energy.json')
const wsUrl = subscriptions.getEventLogsSubscriptionUrl('https://mainnet.vechain.org', {
  address: '0x0000000000000000000000000000456e65726779',  // VTHO
  topics: ['0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef']  // Transfer topic0
});
const ws = new WebSocket(wsUrl);
ws.onmessage = (msg) => {
  const logs = JSON.parse(msg.data);
  console.log('VTHO Transfer:', logs);  // Decode with ABIEvent
};

import { subscriptions } from '@vechain/sdk-network';
import WebSocket from 'ws';
// Fetch ABI: await fetch('https://raw.githubusercontent.com/vechain/b32/master/ABIs/energy.json')
const wsUrl = subscriptions.getEventLogsSubscriptionUrl('https://mainnet.vechain.org', {
  address: '0x0000000000000000000000000000456e65726779',  // VTHO
  topics: ['0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef']  // Transfer topic0
});
const ws = new WebSocket(wsUrl);
ws.onmessage = (msg) => {
  const logs = JSON.parse(msg.data);
  console.log('VTHO Transfer:', logs);  // Decode with ABIEvent
};

import { subscriptions } from '@vechain/sdk-network';
import WebSocket from 'ws';
// Fetch ABI: await fetch('https://raw.githubusercontent.com/vechain/b32/master/ABIs/energy.json')
const wsUrl = subscriptions.getEventLogsSubscriptionUrl('https://mainnet.vechain.org', {
  address: '0x0000000000000000000000000000456e65726779',  // VTHO
  topics: ['0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef']  // Transfer topic0
});
const ws = new WebSocket(wsUrl);
ws.onmessage = (msg) => {
  const logs = JSON.parse(msg.data);
  console.log('VTHO Transfer:', logs);  // Decode with ABIEvent
};

Multi-connect: Open separate WS for events + blocks. No polling needed!
Ears open!

PRO TIP

No ABI? Can't decode—fetch from b32.

Another perk for you, the topic you find in the example above is common to ALL ERC20 tokens!

2. Blocks & Beats

4. Tx Pool Watch

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