Chain Fundamentals

import { Chain } from 'tevm';

// Lookup by chain ID
const mainnet = Chain.fromId(1);
const sepolia = Chain.fromId(11155111);
const polygon = Chain.fromId(137);

console.log(mainnet?.name);  // "Ethereum Mainnet"
console.log(sepolia?.name);  // "Sepolia"
console.log(polygon?.name);  // "Polygon Mainnet"

// Without chain ID: Transaction could be replayed on any network
const tx = {
  to: "0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb2",
  value: "1000000000000000000", // 1 ETH
  nonce: 5,
  gasPrice: "20000000000",
  gasLimit: "21000"
};

// Signed on mainnet, but could be replayed on:
// - Goerli (same addresses exist)
// - Private network (if you have funds there)
// - ANY network with identical account state

import { Transaction } from 'tevm';

// Chain ID embedded in signature
const mainnetTx = Transaction.fromLegacy({
  to: "0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb2",
  value: "1000000000000000000",
  nonce: 5,
  gasPrice: "20000000000",
  gasLimit: "21000",
  chainId: 1  // Mainnet only - cannot be replayed on other networks
});

const sepoliaTx = Transaction.fromLegacy({
  to: "0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb2",
  value: "1000000000000000000",
  nonce: 5,
  gasPrice: "20000000000",
  gasLimit: "21000",
  chainId: 11155111  // Sepolia only - different signature than mainnet
});

// Same transaction parameters, different signatures due to chain ID

import { Transaction } from 'tevm';
import { secp256k1 } from 'tevm/crypto';

const privateKey = Bytes32(); // Your private key

// Create transaction for specific network
const tx = Transaction.fromEIP1559({
  to: "0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb2",
  value: "1000000000000000000",
  nonce: 0,
  chainId: 1,  // Mainnet
  maxFeePerGas: "30000000000",
  maxPriorityFeePerGas: "2000000000",
  gasLimit: "21000"
});

// Sign with chain ID included in signature
const signed = tx.sign(privateKey);

// Extract chain ID from signed transaction
console.log(signed.chainId);  // 1 (mainnet)

// This transaction can ONLY be broadcast to mainnet
// Attempting to broadcast to Sepolia will fail

import { Chain } from 'tevm';

function identifyNetwork(chainId: number): string {
  const chain = Chain.fromId(chainId);
  if (!chain) return "Unknown network";

  // Check network type
  if (chainId === 1) return "Ethereum Mainnet (Production)";
  if ([11155111, 5, 3, 4, 42].includes(chainId)) return "Ethereum Testnet";
  if ([137, 10, 42161, 8453].includes(chainId)) return "Layer 2 Network";

  return chain.name;
}

console.log(identifyNetwork(1));        // "Ethereum Mainnet (Production)"
console.log(identifyNetwork(11155111)); // "Ethereum Testnet"
console.log(identifyNetwork(137));      // "Layer 2 Network"

import { Transaction, Chain } from 'tevm';

function validateNetwork(tx: Transaction, expectedChainId: number): boolean {
  if (tx.chainId !== expectedChainId) {
    const expected = Chain.fromId(expectedChainId);
    const actual = Chain.fromId(tx.chainId);
    throw new Error(
      `Network mismatch: expected ${expected?.name} (${expectedChainId}), ` +
      `got ${actual?.name} (${tx.chainId})`
    );
  }
  return true;
}

// Example: Validate mainnet transaction
const tx = Transaction.fromEIP1559({
  to: "0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb2",
  value: "1000000000000000000",
  chainId: 1,  // Mainnet
  maxFeePerGas: "30000000000",
  maxPriorityFeePerGas: "2000000000",
  gasLimit: "21000"
});

validateNetwork(tx, 1);  // ✓ Pass
validateNetwork(tx, 11155111);  // ✗ Throws: Network mismatch

import { Chain } from 'tevm';

function isTestnet(chainId: number): boolean {
  // Known testnets
  const testnets = [
    11155111,  // Sepolia
    5,         // Goerli (deprecated)
    3,         // Ropsten (deprecated)
    4,         // Rinkeby (deprecated)
    42,        // Kovan (deprecated)
    17000,     // Holesky
    84532,     // Base Sepolia
    421614,    // Arbitrum Sepolia
    11155420,  // Optimism Sepolia
    80002      // Polygon Amoy
  ];

  return testnets.includes(chainId);
}

console.log(isTestnet(1));        // false (mainnet)
console.log(isTestnet(11155111)); // true  (Sepolia)
console.log(isTestnet(137));      // false (Polygon mainnet)

import { Chain, Transaction } from 'tevm';

// Network identification: Get chain metadata
const chain = Chain.fromId(1);
console.log(chain?.name);                      // "Ethereum Mainnet"
console.log(chain?.nativeCurrency.symbol);     // "ETH"
console.log(chain?.rpc[0]);                    // RPC endpoint
console.log(chain?.explorers?.[0].url);        // "https://etherscan.io"

// Replay protection: Chain ID in transaction signature
const tx = Transaction.fromEIP1559({
  to: "0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb2",
  chainId: 1,  // Signed into transaction - prevents replay
  // ... other fields
});

// Chain metadata helps you:
// - Display network name to users
// - Connect to correct RPC endpoint
// - Link to block explorers
// - Show correct currency symbols

// Chain ID in signature ensures:
// - Transaction only valid on intended network
// - Cannot be replayed on other chains
// - Network-specific transaction validity