Nerdiest Political Manifesto

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    A module to store and interact with blocks.

    Note: this README reflects the state of the library from v5.0.0 onwards. See README from the standalone repository for an introduction on the last preceding release.


    To obtain the latest version, simply require the project using npm:

    npm install @ethereumjs/blockchain



    The Blockchain package represents an Ethereum-compatible blockchain storing a sequential chain of @ethereumjs/block blocks and holding information about the current canonical head block as well as the context the chain is operating in (e.g. the hardfork rules the current head block adheres to).

    New blocks can be added to the blockchain. Validation ensures that the block format adheres to the given chain rules (with the Blockchain.validateBlock() function) and consensus rules (Blockchain.consensus.validateConsensus()).

    The library also supports reorg scenarios e.g. by allowing to add a new block with Blockchain.putBlock() which follows a different canonical path to the head than given by the current canonical head block.


    The following is an example to iterate through an existing Geth DB (needs level to be installed separately).

    This module performs write operations. Making a backup of your data before trying it is recommended. Otherwise, you can end up with a compromised DB state.

    import { Blockchain } from '@ethereumjs/blockchain'
    import { Chain, Common } from '@ethereumjs/common'
    const { Level } = require('level')
    const gethDbPath = './chaindata' // Add your own path here. It will get modified, see remarks.
    const common = new Common({ chain: Chain.Ropsten })
    const db = new Level(gethDbPath)
    // Use the safe static constructor which awaits the init method
    const blockchain = Blockchain.create({ common, db })
    blockchain.iterator('i', (block) => {
      const blockNumber = block.header.number.toString()
      const blockHash = block.hash().toString('hex')
      console.log(`Block ${blockNumber}: ${blockHash}`)

    WARNING: Since @ethereumjs/blockchain is also doing write operations on the DB for safety reasons only run this on a copy of your database, otherwise this might lead to a compromised DB state.


    Starting with v6 there is a dedicated consensus class for each type of supported consensus, Ethash, Clique and Casper (PoS, this one is rather the do-nothing part of Casper and letting the respective consensus/beacon client do the hard work! 🙂). Each consensus class adheres to a common interface Consensus implementing the following five methods in a consensus-specific way:

    • genesisInit(genesisBlock: Block): Promise<void>
    • setup(): Promise<void>
    • validateConsensus(block: Block): Promise<void>
    • validateDifficulty(header: BlockHeader): Promise<void>
    • newBlock(block: Block, commonAncestor?: BlockHeader, ancientHeaders?: BlockHeader[]): Promise<void>

    Custom Conensus Algorithms

    Also part of V6, you can also create a custom consensus class implementing the above interface and pass it into the Blockchain constructor using the consensus option at instantiation. See this test script for a complete example of how write and use a custom consensus implementation.

    Note, if you construct a blockchain with a custom consensus implementation, transition checks for switching from PoW to PoS are disabled so defining a merge hardfork will have no impact on the consensus mechanism defined for the chain.

    Custom Genesis State

    Starting with v6 responsibility for setting up a custom genesis state moved from the Common library to the Blockchain package, see PR #1924 for some work context.

    A genesis state can be set along Blockchain creation by passing in a custom genesisBlock and genesisState. For mainnet and the official test networks like sepolia or goerli genesis is already provided with the block data coming from @ethereumjs/common. The genesis state is being integrated in the Blockchain library (see genesisStates folder).

    TODO: add code example here!

    The genesis block from the initialized Blockchain can be retrieved via the Blockchain.genesisBlock getter. For creating a genesis block from the params in @ethereumjs/common, the createGenesisBlock(stateRoot: Buffer): Block method can be used.

    EIP-1559 Support

    This library supports the handling of EIP-1559 blocks and transactions starting with the v5.3.0 release.



    Generated TypeDoc API Documentation

    BigInt Support

    Starting with v6 the usage of BN.js for big numbers has been removed from the library and replaced with the usage of the native JS BigInt data type (introduced in ES2020).

    Please note that number-related API signatures have changed along with this version update and the minimal build target has been updated to ES2020.


    For debugging blockchain control flows the debug library is used and can be activated on the CL with DEBUG=[Logger Selection] node [Your Script to Run].js.

    The following initial logger is currently available:

    Logger Description
    blockchain:clique Clique operations like updating the vote and/or signer list

    The following is an example for a logger run:

    Run with the clique logger:

    DEBUG=blockchain:clique ts-node test.ts


    See our organizational documentation for an introduction to EthereumJS as well as information on current standards and best practices. If you want to join for work or carry out improvements on the libraries, please review our contribution guidelines first.




    npm i @ethereumjs/blockchain

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