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In this Recipe, we leverage the web3.js library to monitor real-time incoming transactions to a specified address.We’ll use a WebSocket endpoint to listen for new blocks, then inspect the new block to find transactions we might be interested in.
Install node.js in case it is not installed yet.Create a new directory for your project, then install the web3.js library:npm install web3
To run this code, you will need a Chainstack account and an Ethereum archive node.
  1. Sign up with Chainstack.
  2. Deploy a node.
  3. View node access and credentials.
Here is a breakdown of the code:
  1. Import and Setup:
    • The Web3 class is imported from the web3 package.
    • A new Web3 instance is created, connected to an Ethereum node through a WebSocket URL (NODE_URL).
    • A specific Ethereum wallet address to monitor is defined as walletAddress.
  2. Subscribing to New Block Headers:
    • The function subscribeToNewBlocks is an asynchronous function that establishes a subscription to the newBlockHeaders event using web3.eth.subscribe.
    • Upon successfully subscribing, it logs the connection status and the subscription ID.
    • It attaches two event listeners to the subscription: one for handling new block data (data event) and another for handling errors (error event).
  3. Handling New Blocks:
    • The handleNewBlock function is triggered whenever a new block header is received.
    • It logs a message indicating it’s scanning for transactions to the specified walletAddress.
    • The function fetches the full block data, including all transactions, using web3.eth.getBlock.
    • It iterates over each transaction in the block, checking if the transaction’s recipient (to address) matches the walletAddress.
    • For transactions matching the criteria, it logs the transaction hash, sender address (from), recipient address (to), and the value transferred in Ether.
  4. Error Handling:
    • The handleError function logs any errors that occur during the subscription or block handling process.
  5. Execution:
    • The script executes by calling subscribeToNewBlocks(), initiating the subscription and monitoring process.
Now you can get your endpoint and paste it into the NODE_URL const. Then you can run it with node YOUR_SCRIPT_NAME
import { Web3 } from "web3";

const NODE_URL =
	"YOUR_WEBSOCKET_USER";
const web3 = new Web3(NODE_URL);

const walletAddress = "ADDRESS_TO_MONITOR";

async function subscribeToNewBlocks() {
  try {
    const event = "newBlockHeaders";
    const subscription = await web3.eth.subscribe(event);

    console.log(`Connected to ${event}, Subscription ID: ${subscription.id}`);

    // Attach an event listener to the subscription object for 'data'
    subscription.on("data", handleNewBlock);
    subscription.on("error", handleError);
  } catch (error) {
    console.error(`Error subscribing to new blocks: ${error}`);
  }
}

async function handleNewBlock(blockHeader) {
  console.log(`Scanning for transactions to: ${walletAddress}`)
  //console.log("New block header:", blockHeader);

  // Fetch the full block data to access transactions
  const block = await web3.eth.getBlock(blockHeader.number, true);

  if (block && block.transactions) {
    block.transactions.forEach((tx) => {
      // Check if the transaction was to MY_ADDRESS
      if (tx.to && tx.to.toLowerCase() === walletAddress.toLowerCase()) {
        console.log("Incoming ETH transfer:", tx.hash);
        console.log(`From: ${tx.from}`);
        console.log(`To: ${walletAddress}`); // To confirm the address monitored
        console.log(`Value: ${web3.utils.fromWei(tx.value, 'ether')} ETH`);
        console.log("--------------------------------");
      }
    });
  }
}

function handleError(error) {
  console.error("Error when subscribing to new block headers:", error);
}

subscribeToNewBlocks();

New subscription: 0x345d18c7ccab37f303282b72638363f3
Got new block: 17793654
Incoming ETH transfer: 0xe339f5353bd5e139a45aa8e42b9c12189d5809ce79a645dccbc2908a70b79421
From: 0xae2Fc483527B8EF99EB5D9B44875F005ba1FaE13
Value: 0.000000000441920915 ETH
--------------------------------
Incoming ETH transfer: 0xcd5488f9985b44c7b4e0de3140c47ade95fa01c9ee5e32adf87d04f1e2afcb27
From: 0xae2Fc483527B8EF99EB5D9B44875F005ba1FaE13
Value: 0.000000000450311043 ETH
--------------------------------