JavaScript / TypeScript

For JavaScript and TypeScript development on the Avalanche C-Chain you have two mature choices: web3.js and ethers.js. Both are actively maintained and both speak standard EVM JSON-RPC, so either connects to https://avalanche.therpc.io/YOUR_API_KEY at chain ID 43114 with AVAX as gas. For new projects we recommend ethers.js v6: it has first-class TypeScript support and a smaller bundle, which matters for browser dApps interacting with Avalanche DeFi like Trader Joe or GMX.

Both web3.js and ethers.js are actively maintained and production-ready against the C-Chain. For new Avalanche projects, ethers.js v6 is the recommended starting point thanks to its stronger TypeScript support and smaller bundle size.

Web3.js

web3.js is the original and one of the most widely used JavaScript APIs for EVM chains, and it works against the Avalanche C-Chain unchanged. Install it with npm install web3, then instantiate new Web3('https://avalanche.therpc.io/YOUR_API_KEY') to get a client for reading AVAX balances and sending transactions on chain 43114.

1import Web3 from 'web3';
2const web3 = new Web3('https://avalanche.therpc.io/YOUR_API_KEY');
3 
4// Get balance
5const getBalance = async (address) => {
6	const balance = await web3.eth.getBalance(address);
7	const balanceInEth = web3.utils.fromWei(balance, 'ether');
8	return balanceInEth;
9};
10 
11// Send transaction
12const sendTransaction = async (from, to, value) => {
13	const tx = {
14		from,
15		to,
16		value: web3.utils.toWei(value, 'ether'),
17	};
18	return await web3.eth.sendTransaction(tx);
19};

• GitHub: https://github.com/web3/web3.js
• Docs: https://web3js.readthedocs.io/
• Key features: complete EVM API coverage for the Avalanche C-Chain, WebSocket support for subscriptions, contract interactions, ENS resolution, and a large community

Ethers.js

ethers.js is a modern, compact library with first-class TypeScript support, which makes it a strong default for new C-Chain apps. Install it with npm install ethers, then create new ethers.JsonRpcProvider('https://avalanche.therpc.io/YOUR_API_KEY') to connect to the Avalanche C-Chain. The provider handles reads; pair it with a Wallet to sign and send AVAX transactions.

1import { ethers } from 'ethers';
2const provider = new ethers.JsonRpcProvider('https://avalanche.therpc.io/YOUR_API_KEY');
3 
4// Get balance
5const getBalance = async (address) => {
6	const balance = await provider.getBalance(address);
7	return ethers.formatEther(balance);
8};
9 
10// Send transaction
11const sendTransaction = async (wallet, to, value) => {
12	const tx = await wallet.sendTransaction({
13		to,
14		value: ethers.parseEther(value),
15	});
16	return await tx.wait();
17};

• GitHub: https://github.com/ethers-io/ethers.js/
• Docs: https://docs.ethers.org/
• Key features: first-class TypeScript support, smaller bundle size for browser C-Chain dApps, strong security defaults, ENS resolution, and a thoroughly tested codebase

TypeScript Support

Both web3.js and ethers.js ship their own type definitions, so there is no separate @types/* package to install for either one when building C-Chain apps in TypeScript. You get IDE autocompletion across the full API, compile-time checking that catches a wrong argument before it ever reaches the Avalanche endpoint, and type signatures that double as inline documentation.

1import { BigNumber } from 'ethers';
2 
3interface TransactionData {
4	to: string;
5	value: BigNumber;
6	gasLimit?: BigNumber;
7}
8 
9const createTransaction = async (data: TransactionData) => {
10	// Your implementation
11};

Node.js Usage

Both libraries run server-side in Node.js — useful for C-Chain indexers, bots, and backends — and support either CommonJS require() or ESM import depending on how your project is configured. The connection string stays the same https://avalanche.therpc.io/YOUR_API_KEY in either module system.

1// Web3.js in Node.js
2const Web3 = require('web3');
3const web3 = new Web3('https://avalanche.therpc.io/YOUR_API_KEY');
4 
5// Ethers.js in Node.js
6const { ethers } = require('ethers');
7const provider = new ethers.JsonRpcProvider('https://avalanche.therpc.io/YOUR_API_KEY');

Browser Usage

In the browser, import either library as an ES module and let a bundler like webpack or Vite tree-shake and package it for your C-Chain dApp. When the user has MetaMask or another injected wallet, wrap it with new ethers.BrowserProvider(window.ethereum) so the wallet signs AVAX transactions and you can prompt it to switch to the Avalanche C-Chain (43114).

1// Using ES modules
2import { Web3 } from 'web3';
3// or
4import { ethers } from 'ethers';
5 
6// Using window.ethereum (MetaMask)
7const provider = new ethers.BrowserProvider(window.ethereum);