subscribe ("newBlockHeaders") | Ethereum

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Parameters

• string — a keyword identifying the type of event to subscribe to, newBlockHeaders in this case. In ethers.js v6 this maps to the "block" event on a WebSocketProvider.
• function — a listener function that will be called every time a new block is received. With ethers.js v6, the listener receives the block number of the newly added block.

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Response

• object— a block object with the following fields:
  • number — the block number of the requested block, encoded as hexadecimal. null if the block is pending.
  • hash — the block hash of the requested block. null if the block pending.
  • parenthash — hash of the previous block used to generate the current block. Also known as the ‘parent block’.
  • nonce — the hash used to demonstrate proof-of-work. null if the block pending. It returns 0x0000000000000000 when the consensus is proof-of-stake.
  • sha3uncles — the hash of the list of uncles included in the block. It is used to identify the block uniquely and to verify the integrity of the block’s data.
  • logsbloom — the bloom filter for the logs of the block, a data structure that allows for efficient membership testing of elements in a set, in this case, the logs included in the block. null if pending.
  • transactionsroot — the root of the transaction trie of the block. The transactionsRoot field allows Ethereum nodes to verify the integrity of the transactions in a block.
  • stateroot — the root of the final state trie of the block. The stateroot field is included in the block header and is used to verify the integrity of the state at the time the block was processed
  • receiptsroot — the root of the receipts trie of the block. A 32-byte hash of the root node of the receipts trie of all transactions in the block. It is used to verify the integrity of the receipts data for all transactions in the block.
  • miner — the address of the miner receiving the reward.
  • difficulty — a measure of how hard it is to find a valid block for the Ethereum blockchain. It is a number that increases as more miners join the network and more blocks are added to the chain, encoded as hexadecimal.
  • totaldifficulty — the cumulative sum of the difficulty of all blocks that have been mined in the Ethereum network since the inception of the network. It measures the overall security and integrity of the Ethereum network.
  • extradata — extra data included in a block by the miner who mined it. It often includes messages or other information related to the block.
  • size — the size of this block in bytes as an integer value, encoded as hexadecimal.
  • gaslimit — the maximum gas allowed in this block, encoded as hexadecimal.
  • gasused — the total used gas by all transactions in this block, encoded as hexadecimal.
  • timestamp — the Unix timestamp for when the block was collated.
  • transactions — an array of transaction objects. See eth_getTransactionByHash for the exact shape.
  • uncles — an array of uncle hashes.

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subscribe("newBlockHeaders") code example

• provider.on("block", listener) — fires for each new block and passes the block number to the listener.
• provider.on("error", listener) — fires if an error is detected on the connection.
• provider.off("block", listener) — removes a single listener for the "block" event.
• provider.removeAllListeners() — removes every listener, which effectively unsubscribes.

const { ethers } = require("ethers");

const NODE_URL = "CHAINSTACK_WSS_ENDPOINT";
const provider = new ethers.WebSocketProvider(NODE_URL);

async function subscribeToNewBlocks() {
  try {
    // Subscribe to new blocks by listening for the 'block' event
    provider.on("block", handleNewBlock);
    provider.on("error", handleError);

    console.log("Connected to the 'block' event");
  } catch (error) {
    console.error(`Error subscribing to new blocks: ${error}`);
  }
}

// Listener functions to react to the different events

// Listener that fetches and logs the full block for each new block number
async function handleNewBlock(blockNumber) {
  const blockHeader = await provider.getBlock(blockNumber);
  console.log("New block header:", blockHeader);
}

// Listener that logs any errors that occur
function handleError(error) {
  console.error("Error when subscribing to new block header:", error);
}

subscribeToNewBlocks();

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Use case

const { ethers } = require("ethers");
const NODE_URL = "CHAINSTACK_WSS_URL";
const provider = new ethers.WebSocketProvider(NODE_URL);

let blockCount = 0;

async function subscribeToNewBlocks() {
  try {
    // Subscribe to new blocks by listening for the 'block' event
    provider.on("block", handleNewBlock);
    provider.on("error", handleError);
    console.log("Subscribed to the 'block' event");
  } catch (error) {
    console.error(`Error subscribing to new blocks: ${error}`);
  }
}

async function unsubscribeFromNewBlocks() {
  await provider.removeAllListeners();
  console.log("Successfully unsubscribed from new blocks");
  return process.exit(1);
}

/* Listener functions to react to the different events */

// Listener that extracts block number and base fee per gas from the received block
async function handleNewBlock(blockNumber) {
  const blockHeader = await provider.getBlock(blockNumber);
  const baseFeePerGas = ethers.formatUnits(blockHeader.baseFeePerGas, "gwei");

  blockCount++;
  console.log(
    `Block number: ${blockNumber} \nBase Fee per Gas: ${baseFeePerGas} Gwei \n`
  );
  if (blockCount === 100) {
    unsubscribeFromNewBlocks();
  }
}

// Listener that logs any errors that occur
function handleError(error) {
  console.error(`Error receiving new blocks: ${error}`);
}

subscribeToNewBlocks();