Skip to main content


web3.js is a JavaScript library for building on EVM blockchains.


To install web3.js run the following command:

npm i web3


web3.js v4 supports both CJS ( CommonJS ) and native ESM module imports. For importing the main Web3 class in CJS you can use:

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

and for ESM style imports, you can use:

import { Web3 } from 'web3';

Connecting to Telos

You must initialize the Web3 object with a provider, otherwise, you won't be able to fully use web3.js functionalities. Here is an example of creating a web3 instance with an HTTP provider:

import { Web3 } from 'web3';

// RPC endpoint
// use for testnet
const web3 = new Web3(''); 

Interacting With Telos

Querying State

After instantiating the web3 instance with a new Web3 provider, we can access the web3.eth package to fetch data from the blockchain:

// get last block number
await web3.eth.getBlockNumber();
// ↳ 338037822

// get the chain id of the current provider
await web3.eth.getChainId();
// ↳ 40

Sending Transactions

//add an account to a wallet
const account = web3.eth.accounts.wallet.add('0x50d349f5cf627d44858d6fcb6fbf15d27457d35c58ba2d5cfeaf455f25db5bec');

//create transaction object to send 1 tlos to '0xa32...c94' address from the account[0]
const tx = 
    from: account[0].address,
    to: '0xa3286628134bad128faeef82f44e99aa64085c94', 
    value: web3.utils.toWei('1', '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)
// ↳ Tx hash: 0x03c844b069646e08af1b6f31519a36e3e08452b198ef9f6ce0f0ccafd5e3ae0e

Interacting With a Smart Contract

Instantiate a Contract

The first step to interact with a contract is to instantiate the contract, for which we will need the ABI and the address of the contract

//WTLOS token example
const address = '0xD102cE6A4dB07D247fcc28F366A623Df0938CA9E'

//you can find the complete ABI in
const ABI = 
    //EXample contract ABI
      name: 'symbol',
      outputs: [{ type: 'string' }],
      type: 'function',
      name: 'totalSupply',
      outputs: [{ type: 'uint256' }],
      type: 'function',

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


//make the call to the contract (assuming its an ERC20)
const symbol = await tokenContract.methods.symbol().call();

console.log('Token symbol:',symbol);
// ↳ Token symbol: WTLOS

//make the call to the contract
const totalSupply = await tokenContract.methods.totalSupply().call();

console.log('Token Total supply:', totalSupply);
// ↳ Uniswap Total Supply: TOTAL SUPPLY

//use web3 utils to format the units
console.log(web3.utils.fromWei(totalSupply, 'ether'))
// ↳ 1000000000


//address to send the token
const to = '0xcf185f2F3Fe19D82bFdcee59E3330FD7ba5f27ce';

//value to transfer (1 with 18 decimals)
const value = web3.utils.toWei('1','ether');

//send the transaction => return the Tx receipt
const txReceipt = await tokenContract.methods.transfer(to,value).send({from: account[0].address});

console.log('Tx hash:',txReceipt.transactionHash);
// ↳ Tx hash: HASH