Web3.JS

Web3.js – The JavaScript Library for Interacting with Ethereum 🚀

Introduction

Web3.js is a JavaScript library that allows developers to interact with Ethereum blockchain and smart contracts using JavaScript or Node.js. It acts as a bridge between decentralized applications (dApps) and the Ethereum network, enabling functionalities such as sending transactions, reading blockchain data, and executing smart contracts.

Key Features of Web3.js

• Connect to Ethereum Nodes – Interact with Ethereum using providers like MetaMask, Infura, Alchemy, or local nodes (Geth, Hardhat, Ganache).

• Smart Contract Integration – Deploy and call smart contract functions.

• Send and Sign Transactions – Transfer Ether and tokens between wallets.

• Account Management – Generate and manage Ethereum wallets.

• Event Listening – Listen for blockchain events (logs, transactions).

• Works with Multiple Ethereum Networks – Supports Mainnet, Testnets (Goerli, Sepolia), and Private Networks.

Installation

You can install Web3.js using npm or yarn:

npm install web3
# OR
yarn add web3

Connecting to the Ethereum Network

Web3.js requires a provider to connect to the blockchain. You can use:

• MetaMask (Browser extension)

• Infura/Alchemy (Remote nodes)

• Geth or Ganache (Local nodes)

Example: Connect Using MetaMask

import Web3 from "web3";

const web3 = new Web3(window.ethereum);  // Connects to MetaMask
await window.ethereum.request({ method: "eth_requestAccounts" }); // Request user to connect wallet

console.log("Connected account:", await web3.eth.getAccounts());

Example: Connect Using Infura

const web3 = new Web3("https://mainnet.infura.io/v3/YOUR_INFURA_PROJECT_ID");
web3.eth.getBlockNumber().then(console.log); // Fetch latest block number

Interacting with Ethereum Accounts

1. Get User Accounts

const accounts = await web3.eth.getAccounts();
console.log("Accounts:", accounts);

1. Get ETH Balance

const balance = await web3.eth.getBalance(accounts[0]);
console.log("Balance (in Wei):", balance);
console.log("Balance (in ETH):", web3.utils.fromWei(balance, "ether"));

Sending Ethereum Transactions

Example: Sending Ether

const sender = "0xYourWalletAddress";
const receiver = "0xReceiverAddress";
const amount = web3.utils.toWei("0.1", "ether"); // Convert ETH to Wei

const transaction = await web3.eth.sendTransaction({
  from: sender,
  to: receiver,
  value: amount
});

console.log("Transaction Hash:", transaction.transactionHash);

Interacting with Smart Contracts

Example: Calling a Smart Contract Function

Assume we have a SimpleStorage.sol smart contract deployed with a function getValue()

const contractABI = [/* ABI JSON here */];
const contractAddress = "0xYourContractAddress";

const contract = new web3.eth.Contract(contractABI, contractAddress);
const value = await contract.methods.getValue().call();
console.log("Stored Value:", value);

Example: Writing to a Smart Contract

await contract.methods.setValue(42).send({ from: accounts[0] });
console.log("Updated Smart Contract Value!");

Listening to Events in Web3.js

Smart contracts emit events that can be listened to using Web3.js.

contract.events.ValueUpdated({}, (error, event) => {
  if (!error) {
    console.log("Value Updated:", event.returnValues);
  }
});

Alternative Web3 Libraries

Ethers.js – A lightweight and modern alternative to Web3.js. Viem.js – A newer, type-safe Web3 library for interacting with Ethereum.

Conclusion

Web3.js is a powerful tool for building Ethereum-based applications (dApps). It allows developers to interact with the blockchain, send transactions, call smart contracts, and listen to events easily.

Use Web3.js if you are building:

• dApps (Decentralized Apps)

• NFT Marketplaces

• DeFi Applications

• Crypto Wallets