viem TypeScript Ethereum Library¶

Introduction¶

viem is a modular TypeScript library that allows developers to interact with abstractions over the JSON-RPC API, making it easy to interact with Ethereum nodes. Since Moonbeam has an Ethereum-like API available that is fully compatible with Ethereum-style JSON RPC invocations, developers can leverage this compatibility to interact with Moonbeam nodes. For more information on viem, check out their documentation site.

In this guide, you'll learn how to use viem to send a transaction and deploy a contract on the Moonbase Alpha TestNet. This guide can be adapted for Moonbeam, Moonriver, or a Moonbeam development node.

Checking Prerequisites¶

For the examples in this guide, you will need to have the following:

• An account with funds. You can get DEV tokens for testing on Moonbase Alpha once every 24 hours from the Moonbase Alpha Faucet
• To test out the examples in this guide on Moonbeam or Moonriver, you will need to have your own endpoint and API key, which you can get from one of the supported Endpoint Providers

Installing viem¶

To get started, you'll need to create a basic TypeScript project. First, create a directory to store all of the files you'll be creating throughout this guide, and initialize the project with the following command:

mkdir viem-examples && cd viem-examples && npm init --y

For this guide, you'll need to install the viem library and the Solidity compiler. To install both packages, you can run the following command:

npm install typescript ts-node viem solc@0.8.0

yarn add typescript ts-node viem solc@0.8.0

You can create a TypeScript configuration file by running:

npx tsc --init

Set Up a viem Client (Provider)¶

Throughout this guide, you'll be creating a bunch of scripts that provide different functionality, such as sending a transaction, deploying a contract, and interacting with a deployed contract. In most of these scripts, you'll need to create a viem client to interact with the network.

You can create a viem client for reading chain data, like balances or contract data, using the createPublicClient function, or you can create a viem client for writing chain data, like sending transactions, using the createWalletClient function.

For Reading Chain Data¶

To create a client for reading chain data, you can take the following steps:

1. Import the createPublicClient and http functions from viem and the network you want to interact with from viem/chains. The chain can be any of the following: moonbeam, moonriver, or moonbaseAlpha
2. Create the client using the createPublicClient function and pass in the network and the HTTP RPC endpoint

import { createPublicClient, http } from 'viem';
import { moonbeam } from 'viem/chains';

const rpcUrl = 'INSERT_RPC_API_ENDPOINT'
const publicClient = createPublicClient({
  chain: moonbeam,
  transport: http(rpcUrl),
});

import { createPublicClient, http } from 'viem';
import { moonriver } from 'viem/chains';

const rpcUrl = 'INSERT_RPC_API_ENDPOINT'
const publicClient = createPublicClient({
  chain: moonriver,
  transport: http(rpcUrl),
});

import { createPublicClient, http } from 'viem';
import { moonbaseAlpha } from 'viem/chains';

const rpcUrl = 'https://rpc.api.moonbase.moonbeam.network'
const publicClient = createPublicClient({
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});

import { createPublicClient, http } from 'viem';
import { moonbeamDev } from 'viem/chains';

const rpcUrl = 'http://127.0.0.1:9944'
const publicClient = createPublicClient({
  chain: moonbeamDev,
  transport: http(rpcUrl);
})

For Writing Chain Data¶

To create a client for writing chain data, you can take the following steps:

1. Import the createWalletClient and http functions from viem, the privateKeyToAccount function for loading your accounts via their private keys, and the network you want to interact with from viem/chains. The chain can be any of the following: moonbeam, moonriver, or moonbaseAlpha
2. Create your account using the privateKeyToAccount function
3. Create the client using the createWalletClient function and pass in the account, network, and the HTTP RPC endpoint

import { createWalletClient, http } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { moonbeam } from 'viem/chains';

const account = privateKeyToAccount('INSERT_PRIVATE_KEY');
const rpcUrl = 'INSERT_RPC_API_ENDPOINT'
const walletClient = createWalletClient({
  account,
  chain: moonbeam,
  transport: http(rpcUrl),
});

import { createWalletClient, http } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { moonriver } from 'viem/chains';

const account = privateKeyToAccount('INSERT_PRIVATE_KEY');
const rpcUrl = 'INSERT_RPC_API_ENDPOINT'
const walletClient = createWalletClient({
  account,
  chain: moonriver,
  transport: http(rpcUrl),
});

import { createWalletClient, http } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { moonbaseAlpha } from 'viem/chains';

const account = privateKeyToAccount('INSERT_PRIVATE_KEY');
const rpcUrl = 'https://rpc.api.moonbase.moonbeam.network'
const walletClient = createWalletClient({
  account,
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});

import { createWalletClient, http } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { moonbeamDev } from 'viem/chains';

const account = privateKeyToAccount('INSERT_PRIVATE_KEY');
const rpcUrl = 'http://127.0.0.1:9944'
const walletClient = createWalletClient({
  account,
  chain: moonbeamDev,
  transport: http(rpcUrl),
});

const [account] = await window.ethereum.request({
  method: 'eth_requestAccounts',
});
const walletClient = createWalletClient({
  account,
  chain: moonbeam,
  transport: custom(window.ethereum),
});

Send a Transaction¶

During this section, you'll be creating a couple of scripts. The first one will be to check the balances of your accounts before trying to send a transaction. The second script will actually send the transaction.

You can also use the balance script to check the account balances after the transaction has been sent.

Check Balances Script¶

You'll only need one file to check the balances of both addresses before and after the transaction is sent. To get started, you can create a balances.ts file by running:

touch balances.ts

Next, you will create the script for this file and complete the following steps:

1. Update your imports to include the createPublicClient, http, and formatEther functions from viem and the network you want to interact with from viem/chains
2. Set up a public viem client, which can be used for reading chain data, such as account balances
3. Define the addressFrom and addressTo variables
4. Create the asynchronous balances function that wraps the publicClient.getBalance method
5. Use the publicClient.getBalance function to fetch the balances for the addressFrom and addressTo addresses. You can also leverage the formatEther function to transform the balance into a more readable number (in GLMR, MOVR, or DEV)
6. Lastly, run the balances function

// 1. Imports
import { createPublicClient, http, formatEther } from 'viem';
import { moonbaseAlpha } from 'viem/chains';

// 2. Create a public client for reading chain data
const rpcUrl = 'https://rpc.api.moonbase.moonbeam.network';
const publicClient = createPublicClient({
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});

// 3. Create address variables
const addressFrom = 'INSERT_FROM_ADDRESS';
const addressTo = 'INSERT_TO_ADDRESS';

// 4. Create balances function
const balances = async () => {
  // 5. Fetch balances
  const balanceFrom = formatEther(
    await publicClient.getBalance({ address: addressFrom })
  );
  const balanceTo = formatEther(
    await publicClient.getBalance({ address: addressTo })
  );

  console.log(`The balance of ${addressFrom} is: ${balanceFrom} DEV`);
  console.log(`The balance of ${addressTo} is: ${balanceTo} DEV`);
};

// 6. Call the balances function
balances();

To run the script and fetch the account balances, you can run the following command:

npx ts-node balances.ts

If successful, the balances for the origin and receiving address will be displayed in your terminal in DEV.

Send Transaction Script¶

You'll only need one file to execute a transaction between accounts. For this example, you'll be transferring 1 DEV token from an origin address (from which you hold the private key) to another address. To get started, you can create a transaction.ts file by running:

touch transaction.ts

Next, you will create the script for this file and complete the following steps:

1. Update your imports to include the createWalletClient, http, and parseEther functions from viem, the privateKeyToAccount function from viem/accounts, and the network you want to interact with from viem/chains
2. Set up a viem wallet client for writing chain data, which can be used along with your private key to send transactions. Note: This is for example purposes only. Never store your private keys in a TypeScript file
3. Set up a public viem client for reading chain data, which will be used to wait for the transaction receipt
4. Define the addressTo variable
5. Create the asynchronous send function, which wraps the transaction object and the walletClient.sendTransaction method
6. Use the walletClient.sendTransaction function to sign and send the transaction. You'll need to pass in the transaction object, which only requires the recipient's address and the amount to send. Note that parseEther can be used, which handles the necessary unit conversions from Ether to Wei, similar to using parseUnits(value, decimals). Use await to wait until the transaction is processed and the transaction hash is returned
7. Use the publicClient.waitForTransactionReceipt function to wait for the transaction receipt, signaling that the transaction has been completed. This is particularly helpful if you need the transaction receipt or if you're running the balances.ts script directly after this one to check if the balances have been updated as expected
8. Lastly, run the send function

// 1. Imports
import { createPublicClient, createWalletClient, http, parseEther } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { moonbaseAlpha } from 'viem/chains';

// 2. Create a wallet client for writing chain data
const account = privateKeyToAccount('INSERT_PRIVATE_KEY');
const rpcUrl = 'https://rpc.api.moonbase.moonbeam.network';
const walletClient = createWalletClient({
  account,
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});

// 3. Create a public client for reading chain data
const publicClient = createPublicClient({
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});

// 4. Create to address variable
const addressTo = 'INSERT_ADDRESS';

// 5. Create send function
const send = async () => {
  console.log(
    `Attempting to send transaction from ${account.address} to ${addressTo}`
  );

  // 6. Sign and send tx
  const hash = await walletClient.sendTransaction({
    to: addressTo,
    value: parseEther('1'),
  });

  // 7. Wait for the transaction receipt
  await publicClient.waitForTransactionReceipt({
    hash,
  });

  console.log(`Transaction successful with hash: ${hash}`);
};

// 8. Call the send function
send();

To run the script, you can run the following command in your terminal:

npx ts-node transaction.ts

If the transaction was successful, in your terminal you'll see the transaction hash has been printed out.

You can also use the balances.ts script to check that the balances for the origin and receiving accounts have changed. The entire workflow would look like this:

Deploy a Contract¶

The contract you'll be compiling and deploying in the next couple of sections is a simple incrementer contract, arbitrarily named Incrementer.sol. You can get started by creating a file for the contract:

touch Incrementer.sol

Next, you can add the Solidity code to the file:

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

contract Incrementer {
    uint256 public number;

    constructor(uint256 _initialNumber) {
        number = _initialNumber;
    }

    function increment(uint256 _value) public {
        number = number + _value;
    }

    function reset() public {
        number = 0;
    }
}

The constructor function, which runs when the contract is deployed, sets the initial value of the number variable stored on-chain (the default is 0). The increment function adds the _value provided to the current number, but a transaction needs to be sent, which modifies the stored data. Lastly, the reset function resets the stored value to zero.

Compile Contract Script¶

In this section, you'll create a script that uses the Solidity compiler to output the bytecode and interface (ABI) for the Incrementer.sol contract. To get started, you can create a compile.ts file by running:

touch compile.ts

1. Import the fs and solc packages
2. Using the fs.readFileSync function, you'll read and save the file contents of Incrementer.sol to source
3. Build the input object for the Solidity compiler by specifying the language, sources, and settings to be used
4. Using the input object, you can compile the contract using solc.compile
5. Extract the compiled contract file and export it to be used in the deployment script

// 1. Import packages
const fs = require('fs');
const solc = require('solc');

// 2. Get path and load contract
const source = fs.readFileSync('Incrementer.sol', 'utf8');

// 3. Create input object
const input = {
   language: 'Solidity',
   sources: {
      'Incrementer.sol': {
         content: source,
      },
   },
   settings: {
      outputSelection: {
         '*': {
            '*': ['*'],
         },
      },
   },
};
// 4. Compile the contract
const tempFile = JSON.parse(solc.compile(JSON.stringify(input)));
const contractFile = tempFile.contracts['Incrementer.sol']['Incrementer'];

// 5. Export contract data
export default contractFile;

Deploy Contract Script¶

With the script for compiling the Incrementer.sol contract in place, you can then use the results to send a signed transaction that deploys it. To do so, you can create a file for the deployment script called deploy.ts:

touch deploy.ts

Next, you will create the script for this file and complete the following steps:

1. Update your imports to include the createPublicClient, createWalletClient, and http functions from viem, the privateKeyToAccount function from viem/accounts, the network you want to interact with from viem/chains, and the contractFile from the compile.ts file you created in the Compile Contract Script section
2. Set up a viem wallet client for writing chain data, which will be used along with your private key to deploy the Incrementer contract. Note: This is for example purposes only. Never store your private keys in a TypeScript file
3. Set up a public viem client for reading chain data, which will be used to read the transaction receipt for the deployment
4. Load the contract bytecode and abi for the compiled contract
5. Create the asynchronous deploy function that will be used to deploy the contract via the walletClient.deployContract method
6. Use the walletClient.deployContract function to sign and send the transaction. You'll need to pass in the contract's ABI and bytecode, the account to deploy the transaction from, and the initial value for the incrementer. Use await to wait until the transaction is processed and the transaction hash is returned
7. Use the publicClient.readContract function to get the transaction receipt for the deployment. Use await to wait until the transaction is processed and the contract address is returned
8. Lastly, run the deploy function

// 1. Update imports
import { createPublicClient, createWalletClient, http } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { moonbaseAlpha } from 'viem/chains';
import contractFile from './compile';

// 2. Create a wallet client for writing chain data
// The private key must be prepended with `0x` to avoid errors
const account = privateKeyToAccount('INSERT_PRIVATE_KEY');
const rpcUrl = 'https://rpc.api.moonbase.moonbeam.network';
const walletClient = createWalletClient({
  account,
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});
// 3. Create a public client for reading chain data
const publicClient = createPublicClient({
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});

// 4. Load contract information
const bytecode = contractFile.evm.bytecode.object;
const abi = contractFile.abi;
const _initialNumber = 5;

// 5. Create deploy function
const deploy = async () => {
  console.log(`Attempting to deploy from account: ${account.address}`);

  // 6. Send tx (initial value set to 5)
  const contract = await walletClient.deployContract({
    abi,
    account,
    bytecode,
    args: [_initialNumber],
  });

  // 7. Get the transaction receipt for the deployment
  const transaction = await publicClient.waitForTransactionReceipt({
    hash: contract,
  });

  console.log(`Contract deployed at address: ${transaction.contractAddress}`);
};

// 8. Call the deploy function
deploy();

To run the script, you can enter the following command into your terminal:

npx ts-node deploy.ts

If successful, the contract's address will be displayed in the terminal.

Read Contract Data (Call Methods)¶

Call methods are the type of interaction that doesn't modify the contract's storage (change variables), meaning no transaction needs to be sent. They simply read various storage variables of the deployed contract.

To get started, you can create a file and name it get.ts:

touch get.ts

Then you can take the following steps to create the script:

1. Update your imports to include the createPublicClient and http functions from viem, the network you want to interact with from viem/chains, and the contractFile from the compile.ts file you created in the Compile Contract Script section
2. Set up a public viem client for reading chain data, which will be used to read the current number of the Incrementer contract
3. Create the contractAddress variable using the address of the deployed contract and the abi variable using the contractFile from the compile.ts file
4. Create the asynchronous get function
5. Call the contract using the publicClient.readContract function, passing in the abi, the name of the function, the contractAddress, and any arguments (if needed). You can use await, which will return the value requested once the request promise resolves
6. Lastly, call the get function

// 1. Update imports
import { createPublicClient, http } from 'viem';
import { moonbaseAlpha } from 'viem/chains';
import contractFile from './compile';

// 2. Create a public client for reading chain data
const rpcUrl = 'https://rpc.api.moonbase.moonbeam.network';
const client = createPublicClient({
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});

// 3. Create contract variables
const contractAddress = 'INSERT_CONTRACT_ADDRESS';
const abi = contractFile.abi;

// 4. Create get function
const get = async () => {
  console.log(`Making a call to contract at address: ${contractAddress}`);

  // 5. Call contract
  const data = await client.readContract({
    abi,
    functionName: 'number',
    address: contractAddress,
    args: [],
  });

  console.log(`The current number stored is: ${data}`);
};

// 6. Call get function
get();

To run the script, you can enter the following command in your terminal:

npx ts-node get.ts

If successful, the value will be displayed in the terminal.

Interact with Contract (Send Methods)¶

Send methods are the type of interactions that modify the contract's storage (change variables), meaning a transaction needs to be signed and sent. In this section, you'll create two scripts: one to increment and one to reset the incrementer. To get started, you can create a file for each script and name them increment.ts and reset.ts:

touch increment.ts reset.ts

Open the increment.ts file and take the following steps to create the script:

1. Update your imports to include the createWalletClient and http functions from viem, the network you want to interact with from viem/chains, and the contractFile from the compile.ts file you created in the Compile Contract Script section
2. Set up a viem wallet client for writing chain data, which will be used along with your private key to send a transaction. Note: This is for example purposes only. Never store your private keys in a TypeScript file
3. Set up a public viem client for reading chain data, which will be used to wait for the transaction receipt
4. Create the contractAddress variable using the address of the deployed contract, the abi variable using the contractFile from the compile.ts file, and the _value to increment the contract by
5. Create the asynchronous increment function
6. Call the contract using the walletClient.writeContract function, passing in the abi, the name of the function, the contractAddress, and the _value. You can use await, which will return the transaction hash once the request promise resolves
7. Use the publicClient.waitForTransactionReceipt function to wait for the transaction receipt, signaling that the transaction has been completed. This is particularly helpful if you need the transaction receipt or if you're running the get.ts script directly after this one to check that the current number has been updated as expected
8. Lastly, call the increment function

// 1. Update imports
import { createPublicClient, createWalletClient, http } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { moonbaseAlpha } from 'viem/chains';
import contractFile from './compile';

// 2. Create a wallet client for writing chain data
const account = privateKeyToAccount('INSERT_PRIVATE_KEY');
const rpcUrl = 'https://rpc.api.moonbase.moonbeam.network';
const walletClient = createWalletClient({
  account,
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});

// 3. Create a public client for reading chain data
const publicClient = createPublicClient({
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});

// 4. Create contract variables
const contractAddress = 'INSERT_CONTRACT_ADDRESS';
const abi = contractFile.abi;
const _value = 3;

// 5. Create increment function
const increment = async () => {
  console.log(
    `Calling the increment by ${_value} function in contract at address: ${contractAddress}`
  );
  // 6. Call contract
  const hash = await walletClient.writeContract({
    abi,
    functionName: 'increment',
    address: contractAddress,
    args: [_value],
  });

  // 7. Wait for the transaction receipt
  await publicClient.waitForTransactionReceipt({
    hash,
  });

  console.log(`Tx successful with hash: ${hash}`);
};

// 8. Call increment function
increment();

To run the script, you can enter the following command in your terminal:

npx ts-node increment.ts

If successful, the transaction hash will be displayed in the terminal. You can use the get.ts script alongside the increment.ts script to make sure that value is changing as expected.

Next, you can open the reset.ts file and take the following steps to create the script:

1. Update your imports to include the createWalletClient and http functions from viem, the network you want to interact with from viem/chains, and the contractFile from the compile.ts file you created in the Compile Contract Script section
2. Set up a viem wallet client for writing chain data, which will be used along with your private key to send a transaction. Note: This is for example purposes only. Never store your private keys in a TypeScript file
3. Set up a public viem client for reading chain data, which will be used to wait for the transaction receipt
4. Create the contractAddress variable using the address of the deployed contract and the abi variable using the contractFile from the compile.ts file to increment the contract by
5. Create the asynchronous reset function
6. Call the contract using the walletClient.writeContract function, passing in the abi, the name of the function, the contractAddress, and an empty array for the arguments. You can use await, which will return the transaction hash once the request promise resolves
7. Use the publicClient.waitForTransactionReceipt function to wait for the transaction receipt, signaling that the transaction has been completed. This is particularly helpful if you need the transaction receipt or if you're running the get.ts script directly after this one to check that the current number has been reset to 0
8. Lastly, call the reset function

// 1. Update imports
import { createPublicClient, createWalletClient, http } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { moonbaseAlpha } from 'viem/chains';
import contractFile from './compile';

// 2. Create a wallet client for writing chain data
const account = privateKeyToAccount('INSERT_PRIVATE_KEY');
const rpcUrl = 'https://rpc.api.moonbase.moonbeam.network';
const walletClient = createWalletClient({
  account,
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});

// 3. Create a public client for reading chain data
const publicClient = createPublicClient({
  chain: moonbaseAlpha,
  transport: http(rpcUrl),
});

// 4. Create contract variables
const contractAddress = 'INSERT_CONTRACT_ADDRESS';
const abi = contractFile.abi;

// 5. Create reset function
const reset = async () => {
  console.log(
    `Calling the reset function in contract at address: ${contractAddress}`
  );

  // 6. Call contract
  const hash = await walletClient.writeContract({
    abi,
    functionName: 'reset',
    address: contractAddress,
    args: [],
  });

  // 7. Wait for the transaction receipt
  await publicClient.waitForTransactionReceipt({
    hash,
  });

  console.log(`Tx successful with hash: ${hash}`);
};

// 8. Call reset function
reset();

To run the script, you can enter the following command in your terminal:

npx ts-node reset.ts

If successful, the transaction hash will be displayed in the terminal. You can use the get.ts script alongside the reset.ts script to make sure that value is changing as expected.