# web3.js — Ethereum JavaScript API for DApp Development

> web3.js is a collection of TypeScript libraries that let JavaScript and TypeScript applications interact with Ethereum nodes via JSON-RPC. It handles account management, contract deployment, transaction signing, event subscriptions, and ABI encoding. web3.js is one of the foundational libraries of the Ethereum DApp ecosystem.

## Install

Save as a script file and run:

# web3.js — Ethereum JavaScript API for DApp Development

## Quick Use
```bash
npm install web3

# In your script
# const { Web3 } = require('web3');
# const web3 = new Web3('https://mainnet.infura.io/v3/YOUR_KEY');
# const balance = await web3.eth.getBalance('0x...');
```

## Introduction
web3.js is one of the original JavaScript libraries for interacting with the Ethereum blockchain. Created in 2015, it provides a comprehensive API for reading chain state, sending transactions, deploying contracts, and subscribing to events. It remains widely referenced in tutorials and production DApps.

## What web3.js Does
- Connects to Ethereum nodes via HTTP, WebSocket, or IPC providers
- Encodes and decodes contract calls using ABI definitions
- Signs and sends transactions from local or injected wallets
- Subscribes to real-time events such as new blocks, pending transactions, and log filters
- Provides utility functions for unit conversion, hashing, and address checksum validation

## Architecture Overview
web3.js v4 is a modular TypeScript rewrite organized into packages: `web3-eth` for core chain interaction, `web3-eth-contract` for smart contract abstraction, `web3-eth-accounts` for signing, `web3-utils` for helpers, and `web3-net` for network info. A central `Web3` class ties them together and manages the provider connection. Plugins extend functionality without modifying the core.

## Self-Hosting & Configuration
- Install with `npm install web3` or import individual sub-packages for smaller bundles
- Set the provider to a public RPC endpoint (Infura, Alchemy) or your own Geth/Reth node
- Configure gas price strategies using `web3.eth.calculateFeeData()` for EIP-1559 transactions
- Use `web3.eth.accounts.wallet` to manage local signing keys
- Enable WebSocket provider for real-time subscriptions (`new Web3.providers.WebsocketProvider(url)`)

## Key Features
- Plugin system allows community extensions without forking the core library
- First-class TypeScript support with full type inference on contract methods
- ENS (Ethereum Name Service) resolution built in
- Supports batch JSON-RPC requests for reducing network round trips
- Compatible with browser, Node.js, and React Native environments

## Comparison with Similar Tools
- **ethers.js** — Lighter API with separate provider/signer pattern; web3.js uses a unified Web3 object
- **Viem** — Modern TypeScript-first alternative with tree-shaking; web3.js has broader legacy ecosystem support
- **Wagmi** — React hooks layer built on Viem; web3.js is framework-agnostic
- **Alchemy SDK** — Wraps ethers.js with managed services; web3.js is provider-independent

## FAQ
**Q: Is web3.js still maintained?**
A: The 4.x branch received active development through ChainSafe. The repository is now archived, but the library remains functional and widely used.

**Q: Should I use web3.js or ethers.js for a new project?**
A: For new projects, ethers.js or Viem are generally recommended for their smaller bundle sizes and modern APIs. web3.js is a solid choice if your team already uses it or you rely on its plugin ecosystem.

**Q: Does web3.js work with non-Ethereum chains?**
A: Yes. It works with any EVM-compatible chain (Polygon, BSC, Avalanche) by changing the provider URL.

**Q: How do I handle contract events?**
A: Use `contract.events.EventName()` with a WebSocket provider to receive real-time event logs.

## Sources
- https://github.com/web3/web3.js
- https://docs.web3js.org

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Source: https://tokrepo.com/en/workflows/asset-145b41ca
Author: Script Depot