subscribe ("newBlockHeaders") | Polygon

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Parameters

• string — a keyword identifying the type of event to subscribe to, newBlockHeaders in this case.
• function — (optional) a callback function that will be called every time a new event of the specified type is received. This function takes two parameters: error and result. The error parameter contains any error that occurred while subscribing to the event, and the result parameter contains the data for the event that was received.

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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 Polygon 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 Polygon 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 Polygon network since the inception of the network. It measures the overall security and integrity of the Polygon 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) — registers a listener that activates for each new block; the listener receives the new block number.
• provider.off("block", listener) — removes the listener and stops the subscription.

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

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

/* Listener to react to new block events */

// Event listener that fetches and logs the received block data
async function handleNewBlock(blockNumber) {
    const block = await provider.getBlock(blockNumber);
    console.log(block);
}

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 {
        // Register a listener for the 'block' event
        provider.on('block', handleNewBlock);
        console.log("Subscribed to new blocks");
    } catch (error) {
        console.error(`Error subscribing to new blocks: ${error}`);
    }
}

function unsubscribeFromNewBlocks() {
    provider.off('block', handleNewBlock);
    console.log("Successfully unsubscribed!");
    return process.exit(1);
}

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

// Event listener that extracts block number and base fee per gas from the received block header data
async function handleNewBlock(blockNumber) {

    const block = await provider.getBlock(blockNumber);
    const baseFeeGwei = ethers.formatUnits(block.baseFeePerGas, 'gwei');

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

subscribeToNewBlocks();

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Try the subscribe("newBlockHeaders") RPC method yourself