ChainId

EIP-155 chain identifier for replay protection

Overview

ChainId is a branded number type representing an EIP-155 chain identifier. Used for replay protection and identifying which network a transaction targets.

import * as ChainId from '@voltaire/primitives/ChainId'

const mainnet = ChainId.from(1)
const sepolia = ChainId.from(11155111)

if (ChainId.isMainnet(1)) {
  console.log('Using Ethereum mainnet')
}

Type Definition

type ChainIdType = number & { readonly [brand]: "ChainId" }

The branded type prevents accidentally mixing chain IDs with other numbers.

Creating ChainId

from

Create from a non-negative integer.

const mainnet = ChainId.from(1)
const arbitrum = ChainId.from(42161)
const base = ChainId.from(8453)

Validation: Throws InvalidFormatError if value is not a non-negative integer.

ChainId.from(-1)    // Error: must be non-negative
ChainId.from(1.5)   // Error: must be integer

Constants

Pre-defined chain IDs for common networks:

import { MAINNET, SEPOLIA, HOLESKY, OPTIMISM, ARBITRUM, BASE, POLYGON } from '@voltaire/primitives/ChainId'

// Ethereum
const mainnet = MAINNET      // 1
const sepolia = SEPOLIA      // 11155111
const holesky = HOLESKY      // 17000

// Layer 2s
const optimism = OPTIMISM    // 10
const arbitrum = ARBITRUM    // 42161
const base = BASE            // 8453
const polygon = POLYGON      // 137

GOERLI (5) is deprecated. Use SEPOLIA or HOLESKY for testnet development.

Methods

toNumber

Convert to plain number.

const n = ChainId.toNumber(42161) // 42161

equals

Compare two chain IDs.

const same = ChainId.equals(1, 1)           // true
const different = ChainId.equals(1, 10)     // false

isMainnet

Check if chain ID is Ethereum mainnet.

ChainId.isMainnet(1)     // true
ChainId.isMainnet(10)    // false (Optimism)
ChainId.isMainnet(42161) // false (Arbitrum)

Common Chain IDs

Chain	ID	Type
Ethereum	1	Mainnet
Sepolia	11155111	Testnet
Holesky	17000	Testnet
Optimism	10	L2
Arbitrum One	42161	L2
Base	8453	L2
Polygon	137	Sidechain
Avalanche	43114	L1
BSC	56	L1

EIP-155 Replay Protection

Chain ID is embedded in transaction signatures to prevent replay attacks across chains:

import * as ChainId from '@voltaire/primitives/ChainId'

const tx = {
  chainId: ChainId.from(1),  // Mainnet only
  to: "0x...",
  value: 1000000000000000000n,
  // ... other fields
}

// This transaction can only be valid on Ethereum mainnet
// Submitting to Arbitrum would fail signature verification

Namespace Usage

import { ChainId } from '@voltaire/primitives/ChainId'

// Using namespace object
const id = ChainId.from(1)
const isMain = ChainId.isMainnet(1)
const equal = ChainId.equals(1, 1)

See Also

• Chain - Full chain metadata
• Transaction - Transaction signing
• EIP-155 - Replay protection spec