eth_newPendingTransactionFilter | Ethereum

Ethereum API method that creates a filter that listens for new pending transactions on the blockchain. It returns a filter ID, which can be used to retrieve the results using the eth_getFilterChanges method. The eth_newBlockFilter method is useful for developers who must be notified of new blocks on the blockchain in real time.

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Parameters

• none

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Response

• result — a hexadecimal string representing the ID of the newly created filter

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Code examples

Use the following methods with the filter ID:

• eth_getFilterChanges to retrieve updates
• eth_uninstallFilter to remove the filter

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eth_newPendingTransactionFilter code examples

const ethers = require("ethers");

// Create a ChainstackProvider instance for Ethereum mainnet
const chainstack = new ethers.ChainstackProvider("mainnet");

const createFilter = async () => {
  try {
    const filterId = await chainstack.send(
      "eth_newPendingTransactionFilter",
      []
    );
    console.log(filterId); // the filter ID returned by eth_newFilter
    return filterId;
  } catch (error) {
    console.log(error);
  }
};

createFilter();

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Use case

One way to use the eth_newPendingTransactionFilter method is to listen for new pending transactions at predefined intervals and extract specific data from them. For instance, a decentralized application might check for pending transactions every second and identify those that transfer a value greater than a certain amount of the ETH token. This could be useful for monitoring high-value transactions or detecting potential fraud or security threats in real time.

Here is an implementation of this concept using ethers.js:

const ethers = require("ethers");

// Create a ChainstackProvider instance for Ethereum mainnet
const chainstack = new ethers.ChainstackProvider("mainnet");

// Create a filter using eth_newPendingTransactionFilter
const createFilter = async () => {
  try {
    const filterId = await chainstack.send(
      "eth_newPendingTransactionFilter",
      []
    );
    console.log(filterId); // the filter ID returned by eth_newFilter
    return filterId;
  } catch (error) {
    console.log(error);
  }
};

// Use the filter to extract the value from each transaction
async function getValue(filter) {
  try {
    // Retrieve the list of new pending transactions
    const transactions = await chainstack.send("eth_getFilterChanges", [
      filter,
    ]);

    // Loop through the list of transactions and process each one
    for (const hash of transactions) {
      const receipt = await chainstack.send("eth_getTransactionByHash", [hash]);

      // Check that the receipt is not null and has a non-null value field
      if (receipt && receipt.value != null) {
        const value = receipt.value;
        const decimalValue = BigInt(value).toString();
        const convertedValue = ethers.formatEther(decimalValue);

        // Check if the transferred value is greater than or equal to 100 ETH
        if (convertedValue >= 100) {
          console.log(`This transaction is sending more than 100 ETH`);
          console.log(`Transaction Hash: ${hash}`);
          console.log(`Value transferred: ${convertedValue} \n`);
        }
      }
    }
  } catch (error) {
    console.error(error); // Handle errors that may occur
  }
}

// Main program setting an interval to call the `getValue` function at regular intervals
async function main() {
  const filterId = await createFilter();
  setInterval(getValue, 1000, filterId);
}

main();

This code sets up an Ethereum filter to listen for new pending transactions and extract specific data from them.

The code consists of three functions: createFilter, getValue, and main. Here’s an overview of how each function works:

The createFilter function sets up a new filter using the eth_newPendingTransactionFilter method. It returns the ID of the filter, which can be used to retrieve data from the filter later.

The getValue function retrieves the list of new pending transactions using the eth_getFilterChanges method and loops through each transaction. For each transaction, it retrieves the transaction data using the eth_getTransactionByHash method and checks if the transaction value is greater than or equal to 100 ETH. If the value is above this threshold, the function logs information about the transaction to the console.

The main function sets up the program by first calling the createFilter function to create a new filter and retrieve its ID. It then sets an interval to call the getValue function every 1 second, passing the filter ID as an argument to retrieve the latest transaction data at regular intervals.