# How to bridge assets between Ethereum and DBK Chain use Optimism SDK This tutorial explains how you can use the [Optimism SDK](https://sdk.optimism.io) to bridge ETH from L1 (Ethereum) to L2 (DBK Chain). The Optimism SDK is an easy way to add bridging functionality to your JavaScript-based application. It also provides some safety rails to prevent common mistakes that could cause ETH or ERC-20 tokens to be made inaccessible. ## Dependencies * [node](https://nodejs.org/en/) * [pnpm](https://pnpm.io/installation) ## Create a Demo Project You're going to use the Optimism SDK for this tutorial. Since the Optimism SDK is a [Node.js](https://nodejs.org/en/) library, you'll need to create a Node.js project to use it. ### Make a Project Folder ```bash mkdir op-sample-project cd op-sample-project ``` ### Initialize the Project ```bash pnpm init -y ``` ### Install the Optimism SDK ```bash pnpm add @eth-optimism/sdk ``` ### Install ethers.js ```bash pnpm add ethers@^5 ``` ## 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. ```bash export TUTORIAL_PRIVATE_KEY=0x... ``` ## Import Dependencies Create a new file called `index.js` and import the necessary dependencies. ```javascript const optimism = require("@eth-optimism/sdk") const ethers = require("ethers") ``` ## Initialize the SDK Initialize the SDK with the rpc of the ETH and DBK Chain. ```javascript privateKey = process.env.TUTORIAL_PRIVATE_KEY const l1Provider = new ethers.providers.StaticJsonRpcProvider("your_eth_rpc") const l2Provider = new ethers.providers.StaticJsonRpcProvider("https://rpc.mainnet.dbkchain.io/") const l1Wallet = new ethers.Wallet(privateKey, l1Provider) const l2Wallet = new ethers.Wallet(privateKey, l2Provider) ``` ## Deposit ETH Now that you have some ETH on L1 you can deposit that ETH into the `L1StandardBridge` contract. You'll then receive the same number of ETH on L2 in return. ### Check your wallet balance on L1 See how much ETH you have on L1 so you can confirm that the deposit worked later on. ```javascript console.log((await l1Wallet.getBalance()).toString()) ``` ### Create a CrossChainMessenger instance The Optimism SDK exports a CrossChainMessenger class that makes it easy to interact with the `L1StandardBridge` contract. Create an instance of the CrossChainMessenger class: ```javascript const AddressManager = '0x306402f889035e2Cbd7e396080bf365ADB38B7DC' const L1CrossDomainMessenger = '0xDEfab7699Ed60a863dce4B1095576F6d9EC5d254' const L1StandardBridge = '0x28f1b9F457CB51E0af56dff1d11CD6CEdFfD1977' const OptimismPortal = '0x63CA00232F471bE2A3Bf3C4e95Bc1d2B3EA5DB92' const L2OutputOracle = '0x0341bb689CB8a4c16c61307F4BdA254E1bFD525e' const messenger = new optimism.CrossChainMessenger({ l1ChainId: 1, l2ChainId: 20240603, l1SignerOrProvider: l1Wallet, l2SignerOrProvider: l2Wallet, contracts: { l1: { AddressManager: AddressManager, L1CrossDomainMessenger: L1CrossDomainMessenger, L1StandardBridge: L1StandardBridge, OptimismPortal: OptimismPortal, L2OutputOracle: L2OutputOracle, // Need to be set to zero for this version of the SDK. StateCommitmentChain: ethers.constants.AddressZero, CanonicalTransactionChain: ethers.constants.AddressZero, BondManager: ethers.constants.AddressZero, }, l2: optimism.DEFAULT_L2_CONTRACT_ADDRESSES, } }) ``` ### Deposit your ETH Now you can deposit your ETH into the Standard Bridge contract. You'll deposit a small amount of ETH just to demonstrate the process. ```javascript tx = await messenger.depositETH(ethers.utils.parseEther('0.0042')) await tx.wait() ``` ### Wait for the deposit to be relayed You can use the `waitForMessageStatus` function to wait for the deposit to be relayed to L2. ### Check your wallet balance on L1 You should now have less ETH on L1. ```javascript console.log((await l1Wallet.getBalance()).toString()) ``` ### Check your wallet balance on L2 You should now have more ETH on L2. ```javascript console.log((await l2Wallet.getBalance()).toString()) ``` ## 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. ### Start your withdrawal on L2 The first step to withdrawing ETH from L2 to L1 is to start the withdrawal on L2. ```javascript const withdrawal = await messenger.withdrawETH(ethers.utils.parseEther('0.004')) await withdrawal.wait() ``` ### Check your wallet balance on L2 You should now have less ETH on L2, but your wallet balance on L1 will not have changed yet. ```javascript console.log((await l2Wallet.getBalance()).toString()) ``` ### Wait until the withdrawal is ready to prove The second step to withdrawing ETH from L2 to L1 is to prove to the bridge on L1 that the withdrawal happened on L2. You first need to wait until the withdrawal is ready to prove. ```javascript await messenger.waitForMessageStatus(withdrawal.hash, optimism.MessageStatus.READY_TO_PROVE) ``` This step can take one hour. Feel free to take a quick break while you wait. ### Prove the withdrawal on L1 Once the withdrawal is ready to be proven, you'll send an L1 transaction to prove that the withdrawal happened on L2. ```javascript await messenger.proveMessage(withdrawal.hash) ``` ### Wait until the withdrawal is ready for relay The final step to withdrawing ETH from L2 to L1 is to relay the withdrawal on L1. This can only happen after the fault proof period has elapsed. On OP Mainnet, this takes 7 days. ```javascript await messenger.waitForMessageStatus(withdrawal.hash, optimism.MessageStatus.READY_FOR_RELAY) ``` ### Relay the withdrawal on L1 Once the withdrawal is ready to be relayed you can finally complete the withdrawal process. ```javascript await messenger.finalizeMessage(withdrawal.hash) ``` ### Wait until the withdrawal is relayed Now you simply wait until the message is relayed. ```javascript await messenger.waitForMessageStatus(withdrawal.hash, optimism.MessageStatus.RELAYED) ``` ### Check your wallet balance on L1 You should now have more ETH on L1. ```javascript console.log((await l1Wallet.getBalance()).toString()) ``` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.dbkchain.io/bridge/bridge-sdk.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.