eth-block-tracker

What is eth-block-tracker?

The eth-block-tracker npm package is designed to help developers track the latest blocks on the Ethereum blockchain. It provides a simple interface to subscribe to new block events, poll for new blocks, and manage block tracking efficiently.

What are eth-block-tracker's main functionalities?

Polling for New Blocks

This feature allows you to poll for new blocks on the Ethereum blockchain. The code sample demonstrates how to set up a block tracker that listens for the latest block and logs it to the console.

const EthBlockTracker = require('eth-block-tracker');
const provider = require('eth-provider');
const blockTracker = new EthBlockTracker({ provider: provider() });

blockTracker.on('latest', (block) => {
  console.log('Latest block:', block);
});

blockTracker.start();

Handling Errors

This feature allows you to handle errors that may occur during block tracking. The code sample demonstrates how to set up an error handler that logs errors to the console.

const EthBlockTracker = require('eth-block-tracker');
const provider = require('eth-provider');
const blockTracker = new EthBlockTracker({ provider: provider() });

blockTracker.on('error', (error) => {
  console.error('Error:', error);
});

blockTracker.start();

Custom Polling Interval

This feature allows you to set a custom polling interval for checking new blocks. The code sample demonstrates how to set up a block tracker with a polling interval of 20 seconds.

const EthBlockTracker = require('eth-block-tracker');
const provider = require('eth-provider');
const blockTracker = new EthBlockTracker({ provider: provider(), pollingInterval: 20000 });

blockTracker.on('latest', (block) => {
  console.log('Latest block:', block);
});

blockTracker.start();

Other packages similar to eth-block-tracker

web3

The web3 package is a comprehensive library for interacting with the Ethereum blockchain. It includes functionality for tracking blocks, but also provides a wide range of other features such as contract interaction, account management, and more. Compared to eth-block-tracker, web3 is more feature-rich but may be overkill if you only need block tracking.

ethers

The ethers package is another popular library for interacting with the Ethereum blockchain. It offers similar functionalities to web3, including block tracking, but is known for its smaller size and better performance. Like web3, it provides a broader set of features beyond block tracking.

ethereumjs-blockstream

The ethereumjs-blockstream package is specifically designed for streaming Ethereum blocks. It provides a more focused approach to block tracking compared to web3 and ethers, making it a closer alternative to eth-block-tracker. However, it may not be as widely used or supported as the other two libraries.

README

eth-block-tracker

This module walks the Ethereum blockchain, keeping track of the latest block. It uses a web3 provider as a data source and will continuously poll for the next block.

const createInfuraProvider = require('eth-json-rpc-infura')
const { PollingBlockTracker } = require('eth-block-tracker')

const provider = createInfuraProvider({ network: 'mainnet', projectId: process.env.INFURA_PROJECT_ID })
const blockTracker = new PollingBlockTracker({ provider })

blockTracker.on('sync', ({ newBlock, oldBlock }) => {
  if (oldBlock) {
    console.log(`sync #${Number(oldBlock)} -> #${Number(newBlock)}`)
  } else {
    console.log(`first sync #${Number(newBlock)}`)
  }
})

Methods

new PollingBlockTracker({ provider, pollingInterval, retryTimeout, keepEventLoopActive })

creates a new block tracker with provider as a data source and pollingInterval (ms) timeout between polling for the latest block. If an Error is encountered when fetching blocks, it will wait retryTimeout (ms) before attempting again. If keepEventLoopActive is false, in Node.js it will unref the polling timeout, allowing the process to exit during the polling interval. defaults to true, meaning the process will be kept alive.

getCurrentBlock()

synchronous returns the current block. may be null.

console.log(blockTracker.getCurrentBlock())

async getLatestBlock()

Asynchronously returns the latest block. if not immediately available, it will fetch one.

async checkForLatestBlock()

Tells the block tracker to ask for a new block immediately, in addition to its normal polling interval. Useful if you received a hint of a new block (e.g. via tx.blockNumber from getTransactionByHash). Will resolve to the new latest block when its done polling.

Events

latest

The latest event is emitted for whenever a new latest block is detected. This may mean skipping blocks if there were two created since the last polling period.

blockTracker.on('latest', (newBlock) => console.log(newBlock))

sync

The sync event is emitted the same as "latest" but includes the previous block.

blockTracker.on('sync', ({ newBlock, oldBlock }) => console.log(newBlock, oldBlock))

error

The error event means an error occurred while polling for the latest block.

blockTracker.on('error', (err) => console.error(err))

Changelog

[5.0.0] - 2021-03-25

Changed

• (BREAKING) Refactor exports (#71)
• (BREAKING) Target ES2017, remove ES5 builds (#71)
• Migrate to TypeScript (#71)
• Update various dependencies (#44, #49, #54, #59, #61, #62, #63, #70, #72)

Removed

• Remove unused production dependencies (#60, #68)