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This tutorial explains how you can use Viem to bridge ETH from L1 (Ethereum or Sepolia) to L2 (OP Mainnet or OP Sepolia). Viem is a TypeScript interface for Ethereum that provides low-level stateless primitives for interacting with Ethereum. It offers an easy way to add bridging functionality to your JavaScript-based application. Behind the scenes, Viem uses the Standard Bridge contracts to transfer ETH and ERC-20 tokens. Make sure to check out the Standard Bridge guide if you want to learn more about how the bridge works under the hood.

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Supported networks

Viem supports any of the Superchain networks. The OP Stack networks are included in Viem by default. If you want to use a network that isn’t included by default, you can add it to Viem’s chain configurations.

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Dependencies

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Create a demo project

You’re going to use Viem for this tutorial. Since Viem is a Node.js library, you’ll need to create a Node.js project to use it.
1

Make a project folder

mkdir bridge-eth
cd bridge-eth
2

Initialize the project

pnpm init
3

Install the Viem library

pnpm add viem
Want to create a new wallet for this tutorial? If you have cast installed you can run cast wallet new in your terminal to create a new wallet and get the private key.

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Get ETH on Sepolia

This tutorial explains how to bridge ETH from Sepolia to OP Sepolia. You will need to get some ETH on Sepolia to follow along.
You can use this faucet to get ETH on Sepolia.

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Add a private key to your environment

You need a private key in order to sign transactions. Set your private key as an environment variable with the export command. Make sure this private key corresponds to an address that has ETH on Sepolia. 
export TUTORIAL_PRIVATE_KEY=0x...

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Start the Node REPL

You’re going to use the Node REPL to interact with Viem. To start the Node REPL run the following command in your terminal: 
node
This will bring up a Node REPL prompt that allows you to run JavaScript code.

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Import dependencies

You need to import some dependencies into your Node REPL session.
1

Import Viem and other packages

const { createPublicClient, http, createWalletClient, parseEther, formatEther } = require('viem');
const { sepolia, optimismSepolia } = require('viem/chains');
const { privateKeyToAccount } = require('viem/accounts');
const { getL2TransactionHashes, publicActionsL1, publicActionsL2, walletActionsL1, walletActionsL2 } = require('viem/op-stack');
2

Load private key and set account

const PRIVATE_KEY = process.env.TUTORIAL_PRIVATE_KEY;
const account = privateKeyToAccount(PRIVATE_KEY);
3

Create L1 public client for reading from the Sepolia network

const publicClientL1 = createPublicClient({
    chain: sepolia,
    transport: http("https://rpc.ankr.com/eth_sepolia"),
}).extend(publicActionsL1())
4

Create L1 wallet client for sending transactions on Sepolia

const walletClientL1 = createWalletClient({
    account,
    chain: sepolia,
    transport: http("https://rpc.ankr.com/eth_sepolia"),
}).extend(walletActionsL1());
5

Create L2 public client for interacting with OP Sepolia

const publicClientL2 = createPublicClient({
    chain: optimismSepolia,
    transport: http("https://sepolia.optimism.io"),
}).extend(publicActionsL2());
6

Create L2 wallet client on OP Sepolia

const walletClientL2 = createWalletClient({
    account,
    chain: optimismSepolia,
    transport: http("https://sepolia.optimism.io"),
}).extend(walletActionsL2());

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Get ETH on Sepolia

You’re going to need some ETH on L1 that you can bridge to L2. You can get some Sepolia ETH from this faucet.

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Deposit ETH

Now that you have some ETH on L1 you can deposit that ETH into the OptimismPortalProxy contract. You’ll then receive the same number of ETH on L2 in return.
    Using a smart contract wallet? As a safety measure, depositETH will fail if you try to deposit ETH from a smart contract wallet without specifying a recipient. Add the recipient option to the depositETH call to fix this.

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    Withdraw ETH

    You just bridged some ETH from L1 to L2. Nice! Now you’re going to repeat the process in reverse to bridge some ETH from L2 to L1.

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      Important Considerations

      • Challenge period: The 7-day withdrawal challenge Period is crucial for security.
      • Gas costs: Withdrawals involve transactions on both L2 and L1, each incurring gas fees.
      • Private Key handling: Use secure key management practices in real applications.
      • RPC endpoint security: Keep your API key (or any RPC endpoint) secure.

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      Next Steps

      • Develop a user interface for easier interaction with these bridging functions.
      • Implement robust error handling and retry mechanisms for production use.
      You’ve just deposited and withdrawn ETH using viem/op-stack. You should now be able to write applications that use viem/op-stack to transfer ETH between L1 and L2. Although this tutorial used Sepolia and OP Sepolia, the same process works for Ethereum and OP Mainnet.
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