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    Resources common to all EthereumJS implementations.

    Note: this README reflects the state of the library from v2.0.0 onwards. See README from the standalone repository for an introduction on the last preceeding release.


    npm install @ethereumjs/common


    All parameters can be accessed through the Common class which can be required through the main package and instantiated either with just the chain (e.g. 'mainnet') or the chain together with a specific hardfork provided.

    If no hardfork is provided the common is initialized with the default hardfork.

    Current DEFAULT_HARDFORK: istanbul

    Here are some simple usage examples:

    import Common from '@ethereumjs/common'
    // Instantiate with the chain (and the default hardfork)
    const c = new Common({ chain: 'ropsten' })
    c.param('gasPrices', 'ecAddGas') // 500
    // Chain and hardfork provided
    c = new Common({ chain: 'ropsten', hardfork: 'byzantium' })
    c.param('pow', 'minerReward') // 3000000000000000000
    // Instantiate with an EIP activated
    const c = new Common({ chain: 'mainnet', eips: [2537] })
    // Access genesis data for Ropsten network
    c.genesis().hash // 0x41941023680923e0fe4d74a34bdac8141f2540e3ae90623718e47d66d1ca4a2d
    // Get bootstrap nodes for chain/network
    c.bootstrapNodes() // Array with current nodes

    If the initializing library only supports a certain range of hardforks you can use the supportedHardforks option to restrict hardfork access on the Common instance:

    const c = new Common({
      chain: 'ropsten',
      supportedHardforks: ['byzantium', 'constantinople', 'petersburg'],

    This will e.g. throw an error when a param is requested for an unsupported hardfork and like this prevents unpredicted behaviour.


    See the API documentation for a full list of functions for accessing specific chain and depending hardfork parameters. There are also additional helper functions like paramByBlock (topic, name, blockNumber) or hardforkIsActiveOnBlock (hardfork, blockNumber) to ease blockNumber based access to parameters.


    The Common class is implemented as an EventEmitter and is emitting the following events on which you can react within your code:

    Event Description
    hardforkChanged Emitted when a hardfork change occurs in the Common object



    The chain can be set in the constructor like this:

    const c = new Common({ chain: 'ropsten' })

    Supported chains:

    • mainnet
    • ropsten
    • rinkeby
    • kovan
    • goerli
    • calaveras
    • Private/custom chain parameters

    The following chain-specific parameters are provided:

    • name
    • chainId
    • networkId
    • consensusType (e.g. pow or poa)
    • consensusAlgorithm (e.g. ethash or clique)
    • consensusConfig (depends on consensusAlgorithm, e.g. period and epoch for clique)
    • genesis block header values
    • hardforks block numbers
    • bootstrapNodes list
    • dnsNetworks list (EIP-1459-compliant list of DNS networks for peer discovery)

    To get an overview of the different parameters have a look at one of the chain-specifc files like mainnet.json in the chains directory, or to the Chain type in ./src/types.ts.

    Working with private/custom chains

    There are two distinct APIs available for setting up custom(ized) chains.

    Activate with a single custom Chain setup

    If you want to initialize a Common instance with a single custom chain which is then directly activated you can pass a dictionary - conforming to the parameter format described above - with your custom chain values to the constructor using the chain parameter or the setChain() method, here is some example:

    import myCustomChain from './[PATH]/myCustomChain.json'
    const common = new Common({ chain: myCustomChain })

    If you just want to change certain parameters on a chain configuration it can also be convenient to use the Common.forCustomChain() method. With this method you can base your custom chain configuration with a standard one (so using all the values from baseChain as the default values) and then just provide the parameters you want to override:

    const customChainParams = { name: 'custom', chainId: 123, networkId: 678 }
    const customChainCommon = Common.forCustomChain('mainnet', customChainParams, 'byzantium')

    Initialize using customChains Array

    A second way for custom chain initialization is to use the customChains constructor option. This option comes with more flexibility and allows for an arbitrary number of custom chains to be initialized on a common instance in addition to the already supported ones. It also allows for an activation-independent initialization, so you can add your chains by adding to the customChains array and either directly use the chain option to activate one of the custom chains passed or activate a build in chain (e.g. mainnet) and switch to other chains - including the custom ones - by using Common.setChain().

    import myCustomChain1 from './[PATH]/myCustomChain1.json'
    import myCustomChain2 from './[PATH]/myCustomChain2.json'
    // Add two custom chains, initial mainnet activation
    const common1 = new Common({ chain: 'mainnet', customChains: [ myCustomChain1, myCustomChain2 ] })
    // Somewhat later down the road...
    // Add two custom chains, activate customChain1
    const common1 = new Common({ chain: 'customChain1', customChains: [ myCustomChain1, myCustomChain2 ] })


    The hardfork can be set in constructor like this:

    const c = new Common({ chain: 'ropsten', hardfork: 'byzantium' })

    Active Hardforks

    There are currently parameter changes by the following past and future hardfork by the library supported:

    • chainstart
    • homestead
    • dao
    • tangerineWhistle
    • spuriousDragon
    • byzantium
    • constantinople
    • petersburg (aka constantinopleFix, apply together with constantinople)
    • istanbul (DEFAULT_HARDFORK (v2.0.0 release series))
    • muirGlacier
    • berlin (since v2.2.0)
    • london (since v2.4.0)

    Future Hardforks

    The next upcoming HF shanghai is currently not yet supported by this library.

    Parameter Access

    For hardfork-specific parameter access with the param() and paramByBlock() functions you can use the following topics:

    • gasConfig
    • gasPrices
    • vm
    • pow

    See one of the hardfork files like byzantium.json in the hardforks directory for an overview. For consistency, the chain start (chainstart) is considered an own hardfork.

    The hardfork-specific json files only contain the deltas from chainstart and shouldn't be accessed directly until you have a specific reason for it.


    Starting with the v2.0.0 release of the library, EIPs are now native citizens within the library and can be activated like this:

    const c = new Common({ chain: 'mainnet', eips: [2537] })

    The following EIPs are currently supported:

    • EIP-1559: Fee market change for ETH 1.0 chain
    • EIP-2315: Simple subroutines for the EVM
    • EIP-2537: BLS precompiles
    • EIP-2565: ModExp gas cost
    • EIP-2718: Transaction Types
    • EIP-2929: gas cost increases for state access opcodes
    • EIP-2930: Optional accesss list tx type
    • EIP-3529: Reduction in refunds
    • EIP-3541: Reject new contracts starting with the 0xEF byte
    • EIP-3554: Difficulty Bomb Delay to December 2021 (only PoW networks)

    Bootstrap Nodes

    You can use common.bootstrapNodes() function to get nodes for a specific chain/network.

    Genesis States

    Network-specific genesis files are located in the genesisStates folder.

    Due to the large file sizes genesis states are not directly included in the index.js file but have to be accessed directly, e.g.:

    const mainnetGenesisState = require('@ethereumjs/common/dist/genesisStates/mainnet')

    Or by accessing dynamically:

    const genesisStates = require('@ethereumjs/common/dist/genesisStates')
    const mainnetGenesisState = genesisStates.genesisStateByName('mainnet')
    const mainnetGenesisState = genesisStates.genesisStateById(1) // alternative via network Id


    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 do improvements on the libraries have a look at our contribution guidelines.




    npm i @ethereumjs/common

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