This guide will help you migrate from Web3.js v4 to Viem v2 for interacting with the Ethereum blockchain. The guide provides code examples for both libraries for transition.

To begin migrating from Web3.js to Viem, first install the Viem package:

npm install viem@2

When migrating from Web3.js to Viem, the first step is to update how you connect to the Ethereum network. Both libraries use providers, but their initialization differs.

import Web3 from 'web3';

const web3 = new Web3(providerURL);

To migrate this to Viem, you'll need to replace it with using `createPublicClient()`. This function creates a client for interacting with the Ethereum network.

import { createPublicClient, http } from 'viem';

const client = createPublicClient({ transport: http(providerURL) });

For browser wallet connections like MetaMask, update how you handle the injected provider.

const web3 = new Web3(window.ethereum);

To migrate this to Viem, you'll need to use `createWalletClient()` with `custom()` instead of creating a new Web3 instance.

import { createWalletClient, custom } from 'viem';

import { mainnet } from 'viem/chains';

const client = createWalletClient({

chain: mainnet,

transport: custom(window.ethereum),

});

If your code generates private keys, here’s how to migrate that functionality. In web3.js if you are using:

const privateKey = web3.eth.accounts.create().privateKey;

console.log(privateKey);

To migrate this to Viem, you'll use the `generatePrivateKey()` function from the 'viem/accounts' module.

import { generatePrivateKey } from 'viem/accounts';

const privateKey = generatePrivateKey();

console.log(privateKey);

When migrating from Web3.js to Viem, you'll need to update how you create and manage wallets. The process of adding accounts to wallets differs between the two libraries. In web3.js :

const web3 = new Web3();

const wallet = web3.eth.accounts.wallet.add(privateKey);

console.log(wallet[0].address);

To migrate this to Viem, you'll use privateKeyToAccount() to create an account, and then can pass it to createWalletClient() for using it with client.

import { createWalletClient, http } from 'viem';

import { privateKeyToAccount } from 'viem/accounts';

import { mainnet } from 'viem/chains';

const account = privateKeyToAccount(privateKey);

const client = createWalletClient({

account,

chain: mainnet,

transport: http(),

});

Update how you handle message signing, following is web3.js example:

const signature = web3.eth.accounts.sign('Some data', privateKey).signature;

console.log(signature);

To sign message using Viem, you can use `signMessage()` method.

import { createWalletClient, custom } from 'viem'

import { mainnet } from 'viem/chains'

const walletClient = createWalletClient({

chain: mainnet,

transport: custom(window.ethereum!),

});

const [account] = await walletClient.getAddresses();

const signature = await walletClient.signMessage({

account,

message: 'Some data',

});

When migrating transaction sending code, you'll need to update how transactions are signed and sent.

const tx = await web3.eth.sendTransaction({

from: account,

to: '0x92d3267215Ec56542b985473E73C8417403B15ac',

value: web3.utils.toWei('0.001', 'ether'),

});

In Viem there is `sendTransaction()` function avalible with walletClient.

import { createWalletClient, custom, parseEther } from 'viem'

import { mainnet } from 'viem/chains'

const walletClient = createWalletClient({

chain: mainnet,

transport: custom(window.ethereum!),

});

const [account] = await walletClient.getAddresses();

const hash = await walletClient.sendTransaction({

account,

to: '0x92d3267215Ec56542b985473E73C8417403B15ac',

value: parseEther('0.001')

});

When migrating contract deployment code, you'll need to update from Web3.js's deploy and send pattern:

const contract = new web3.eth.Contract(abi);

const deployTx = await contract

.deploy({

data: bytecode,

arguments: ['constructor param'],

})

.send({

from: account,

gas: '1000000',

});

console.log(deployTx.options.address);

In Viem there is `deployContract()` function that can be used for contracts deployment.

import { createWalletClient, custom } from 'viem';

import { mainnet } from 'viem/chains';

const walletClient = createWalletClient({

chain: mainnet,

transport: custom(window.ethereum),

});

const hash = await walletClient.deployContract({

abi,

account, //given account

args: ['constructor param'],

bytecode: bytecode,

});

When migrating contract method calls, you'll need to update from Web3.js's `contract.methods.someFunction().call()`

const contract = new web3.eth.Contract(ABI, CONTRACT_ADDRESS);

const result = await contract.methods.someFunction().call();

console.log(result);

In Viem `readContract()` function can be used for method calls.

const data = await publicClient.readContract({

address: '0x92d3267215Ec56542b985473E73C8417403B15ac',

abi: wagmiAbi,

functionName: 'tokenTotalSupply',

});

When migrating event handling code, you'll need to update from Web3.js's events code :

const event = contract.events.SomeEvent({ fromBlock: 0 });

event.on('data', resolve);

event.on('error', reject);

In Viem there is `watchContractEvent()` function.

const unwatch = publicClient.watchContractEvent({

address: '0x92d3267215Ec56542b985473E73C8417403B15ac',

abi: wagmiAbi,

eventName: 'Transfer',

args: { from: '0x34d3267215Ec56542b985473E73C8417403B1533' },

onLogs: logs => func(logs),

});

When migrating code that computes Keccak-256 hashes, you'll need to update from Web3.js's utility method:

In Viem there is `keccak256()` function for keccak256.