- Deposited transactions: Also known as deposits, these are transactions initiated on L1 and executed on L2. They can be used to submit arbitrary L2 transactions from L1.
-
Withdrawals: These are cross-domain transactions initiated on L2 and finalized by a transaction executed on L1. They can be used to send arbitrary messages on L1 from L2 via the
OptimismPortal.
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.Dependencies
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.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.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.
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.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:Import dependencies
You need to import some dependencies into your Node REPL session.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.Deposit ETH
Now that you have some ETH on L1, in addition to using the method described in Bridging ETH, you can also deposit ETH using the approach shown in the example below. If you are using a contract account, you should pay attention to Address Aliasing.- depositETH
- Full Code
Check your wallet balance on L1
See how much ETH you have on L1 so you can confirm that the deposit worked later on.
We used
formatEther method from viem to format the balance to ether.Create the deposit transaction
Use buildDepositTransaction to build the deposit transaction parameters on L2.Be sure to understand the meanings of the optional parameters
mint and value. You can also use someone else’s address as the to value if desired.Extract the L2 transaction hash
Extracts the corresponding L2 transaction hash from the L1 receipt, and logs it.
This hash represents the deposit transaction on L2.
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. In addition to the method described in Bridging ETH, you can also withdraw ETH using the example approach shown below.- withdrawETH
- Full Code
Create the withdrawal transaction
Uses
buildInitiateWithdrawal to create the withdrawal parameters.
Converts the withdrawal amount to wei and specifies the recipient on L1.Executing the withdrawal
This sends the withdrawal transaction on L2, which initiates the withdrawal process on L2 and logs a transaction hash for tracking the withdrawal.
Confirming L2 transaction
Wait one hour (max) for the L2 Output containing the transaction to be proposed, and log the receipt, which contains important details like the block number etc.
Wait for withdrawal prove
Next, is to prove to the bridge on L1 that the withdrawal happened on L2. To achieve that, you first need to wait until the withdrawal is ready to prove.Build parameters to prove the withdrawal on the L2.
Prove the withdrawal on the L1
Once the withdrawal is ready to be proven, you’ll send an L1 transaction to prove that the withdrawal happened on L2.
Wait for withdrawal finalization
Before a withdrawal transaction can be finalized, you will need to wait for the finalization period.
This can only happen after the fault proof period has elapsed. On OP Mainnet, this takes 7 days.
We’re currently testing fault proofs on OP Sepolia, so withdrawal times
reflect Mainnet times.
Recommend checking with getWithdrawalStatus before the
waitToProve and waitToFinalize actions.Submitting Arbitrary L2 Transactions from L1
EOAs can submit any transaction on L1 that needs to be executed on L2. This also makes it possible for users to interact with contracts on L2 even when the Sequencer is down. If the caller is a contract on L1, you need to pay attention to Address Aliasing. If you have just completed the Bridging ERC-20 tokens to OP Mainnet tutorial, you can try initiating an ERC-20 transfer transaction on L1 that will be executed on L2.encodeFunctionData and erc20Abi can be imported from Viem.
Use OptimismPortal to Send Arbitrary Messages on L1 from L2
The L2ToL1MessagePasser contract’s initiateWithdrawal function accepts a _target address and _data bytes. These are passed to a CALL opcode on L1 when finalizeWithdrawalTransaction is executed after the challenge period.
This means that, by design, the OptimismPortal contract can be used to send arbitrary transactions on L1, with the OptimismPortal acting as the msg.sender.
Important Considerations
- The purpose of this tutorial is to introduce deposited transactions and withdrawals. You should first consider whether the standard bridge and the messenger meet your use case requirements.
- When working with deposited transactions, consider the implications of Address Aliasing.
- When working with withdrawals, consider that OptimismPortal can send arbitrary messages on L1.
- 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.