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Interacting with the blockchain via web3.js

web3.js is a JavaScript library for building and interacting with EVM-compatible blockchain networks.

You can also use web3.js to interact with smart contracts deployed on the Lisk network.

Install​

To install web3.js run the following command:

npm install --save web3

Import​

Before you can start using web3.js, you need to import it into your project.

Web3.js supports both CommonJS and native ESM module imports.

Add the following line of code to the top of your file to import web3.js:

const { Web3 } = require('web3');

Connecting to Lisk​

You can connect to Lisk by instantiating a new Web3 object with an RPC URL of the Lisk network:

import { Web3 } from 'web3';

// Instantiate a web3 object by passing the RPC URL of Lisk Sepolia.
const web3 = new Web3('https://rpc.sepolia-api.lisk.com');

Reading data from the blockchain​

Once you have created the Web3 object, you can use it to read data from the Lisk network.

For example, you can use the getBlockNumber method to get the latest block:

// Retrieve data from blockchain
async function getLatestBlock() {
    const latestBlock = await web3.eth.getBlockNumber()
    console.log("The latest block's number is:", latestBlock);
}

getLatestBlock();
Complete code example
import { Web3 } from 'web3';

// Instantiate a web3 object by passing the RPC URL of Lisk Sepolia.
const web3 = new Web3('https://rpc.sepolia-api.lisk.com');

// Instantiate a web3 object by passing the RPC URL of Lisk.
// const web3 = new Web3('https://rpc.api.lisk.com');

// Retrieve data from blockchain
async function getLatestBlock() {
    const latestBlock = await web3.eth.getBlockNumber()
    console.log("The latest block's number is:", latestBlock);
}

getLatestBlock();
tip

Web3 provides a wide range of Web3Eth methods that can be used to interact with the blockchain.

Writing data to the blockchain​

To write data to the Lisk network, you need to create a Wallet.

note

A web3.js Wallet is your main entry point if you want to use a private key to do any blockchain operations e.g., sending transactions, etc. It is also called a Signer in other libraries.

You can create a Wallet by instantiating a new Web3 Wallet object and the add private key(s) into it. Such private key(s) can later be used to send transactions on the blockchain.

// Add an account to a wallet
const privateKey = '0x<SENDER_PRIVATE_KEY>';
const account = web3.eth.accounts.wallet.add(privateKey);

// Create transaction object to send '.0001' eth to '0x.....' address from the account[0]
const tx =
{
    from: account[0].address,
    to: '<RECIPIENT_ADDRESS>',
    value: web3.utils.toWei('.0001', 'ether')
};
// The 'from' address must match the one previously added with 'wallet.add'

// Send the transaction
const txReceipt = await web3.eth.sendTransaction(tx);

console.log('Tx hash:', txReceipt.transactionHash)
info

PRIVATE_KEY is the private key of the account that is used to sign and send a transaction using web3.js.

The receiving account's balance will increment by 0.0001 ETH once the transaction execution is successful.

Complete code example
import { Web3 } from 'web3';

// Instantiate a web3 object by passing the RPC URL of Lisk Sepolia.
const web3 = new Web3('https://rpc.sepolia-api.lisk.com');

// Instantiate a web3 object by passing the RPC URL of Lisk.
// const web3 = new Web3('https://rpc.api.lisk.com');

// Add an account to a wallet
const privateKey = '0x<SENDER_PRIVATE_KEY>';
const account = web3.eth.accounts.wallet.add(privateKey);

// Create transaction object to send '.0001' eth to '0x.....' address from the account[0]
const tx =
{
    from: account[0].address,
    to: '<RECIPIENT_ADDRESS>',
    value: web3.utils.toWei('.0001', 'ether')
};
// The 'from' address must match the one previously added with 'wallet.add'

// Send the transaction
const txReceipt = await web3.eth.sendTransaction(tx);

console.log('Tx hash:', txReceipt.transactionHash)

Interacting with smart contracts​

You can use web3.js to interact with a smart contract on Lisk by instantiating a Contract object and passing it the ABI and address of a deployed contract.

In the following sections, we will:

  • Read data from a deployed contract, specifically, we will fetch the name of the contract.
  • Furthermore, we will mint a token, via an already deployed contract.
tip

For an overview of existing public functions for the contract, please check the Read Contract and Write Contract tabs for the specific contract.

Reading from smart contracts​

To read data from a smart contract, one needs to pass the address and abi of the deployed & verfied contract. Once the aforementioned information is passed, any read-only function of the smart contract can be called, as described below:

Fetching the contract's name
// Address of the contract you want to interact with.
const address = '0x108872F713A27bc22ca1db8CEefCAC8CbeDdF9E5';

// Instantiate the contract object
const contract = new web3.eth.Contract(abi, address);

// Call any of the 'Read contract' functions e.g. 'name()'
const contractName = await contract.methods.name().call();

console.log('Contract\'s Name is: ', contractName);
Complete code example
get-contract-name.js
import { Web3 } from 'web3';
import { abi } from './abi.js';

// Instantiate a web3 object by passing the RPC URL of Lisk Sepolia.
const web3 = new Web3('https://rpc.sepolia-api.lisk.com');

// Instantiate a web3 object by passing the RPC URL of Lisk.
// const web3 = new Web3('https://rpc.api.lisk.com');

// Address of the contract you want to interact with.
const address = '0x108872F713A27bc22ca1db8CEefCAC8CbeDdF9E5';

// Instantiate the contract object
const contract = new web3.eth.Contract(abi, address);

// Call any of the 'Read contract' functions e.g. 'name()'
const contractName = await contract.methods.name().call();

console.log('Contract\'s Name is: ', contractName);
Output
Contract's Name is:  Lisk

Writing to smart contracts​

To write data through a contract's method, a few things are required such as:

  • contract's address
  • recipient's address
  • private key of the sender
  • ... and the method's name

Use the following snippet to interact with an already deployed contract's mint() function.

miniting-token.js
// Address of the contract you want to interact with.
const contractAddress = '0x108872F713A27bc22ca1db8CEefCAC8CbeDdF9E5';

// Address of the Recipient account receiving the NFT.
const recipientAddress = 'RECIPIENT_ADDRESS'
const amount = web3.utils.toWei('.0001', 'ether')

// PRIVATE_KEY of the sender's account.
const privateKey = 'PRIVATE_KEY';
const account = web3.eth.accounts.wallet.add(privateKey);

// Instantiate the contract object
const contract = new web3.eth.Contract(abi, contractAddress);

// Send a request to the 'mint()' function to mint a token.
const txReceipt = await contract.methods.mint(recipientAddress, amount).send({ from: account[0].address });

console.log('Tx hash:', txReceipt.transactionHash);
Complete code example
miniting-token.js
import { Web3 } from 'web3';
import { abi } from './abi.js';

// Instantiate a web3 object by passing the RPC URL of Lisk.
const web3 = new Web3('https://rpc.sepolia-api.lisk.com');

// For Lisk network
//const web3 = new Web3('https://rpc.api.lisk.com');

// Address of the contract you want to interact with.
const contractAddress = '0x108872F713A27bc22ca1db8CEefCAC8CbeDdF9E5';

// Address of the Recipient account receiving the NFT.
const recipientAddress = 'RECIPIENT_ADDRESS'
const amount = web3.utils.toWei('.0001', 'ether')

// PRIVATE_KEY of the sender's account.
const privateKey = 'PRIVATE_KEY';
const account = web3.eth.accounts.wallet.add(privateKey);

// Instantiate the contract object
const contract = new web3.eth.Contract(abi, contractAddress);

// Send a request to the 'mint()' function to mint a token.
const txReceipt = await contract.methods.mint(recipientAddress, amount).send({ from: account[0].address });

console.log('Tx hash:', txReceipt.transactionHash);
Output
Transaction hash: 0xe654513f453623d9ce329b575985b7fcd09116325d10150d7cd30dcdedc124a9
info

You can use the transaction hash received above to check the details of the mint transaction on Blockscout Explorer: 0xe654513f453623d9ce329b575985b7fcd09116325d10150d7cd30dcdedc124a9.