Skip to main content

Use web3.js

In this tutorial, you'll send a regular transaction from one account to another using the Web3 JavaScript library.

Prerequisites​

info

You can use MetaMask or similar to create an Ethereum account for testing purposes.

Steps​

1. Fund your Ethereum account​

Use the Infura faucet to load testnet ETH on your Ethereum account for the Sepolia network.

If using a network other than Sepolia, ensure you update your environment file with the network name.

2. Create a project directory​

Create a new directory for your project. This can be done from the command line:

mkdir sendTransaction

Change into the new directory:

cd sendTransaction

3. Install required packages​

Install the web3 and dotenv packages in the project directory.

info

The dotenv package allows you to use a .env file to securely store private environment variables on your local machine.

Install the web3 package:

npm install web3

Install the dotenv package:

npm install dotenv --save

4. Create the .env file​

Create a .env file in your project directory to store the project and Ethereum account details.

ETHEREUM_NETWORK = "sepolia"
INFURA_API_KEY = "<Your-API-Key>"
SIGNER_PRIVATE_KEY = "<Your-Private-Key>"

Ensure you replace the following values in the .env file:

  • <Your-API-Key> with the API key of the Web3 project.
  • <Your-Private-Key> with the private key of your Ethereum account. A transaction must be signed with the sender's private key. Make sure that you prefix the SIGNER_PRIVATE_KEY value with 0x. The private key you export from MetaMask will not be prefixed with 0x.

If using a network other than Sepolia, ensure you update ETHEREUM_NETWORK with the network name.

danger

Never disclose your private key. Anyone with your private keys can steal any assets held in your account.

Here is an example .env file showing the valid prefix 0x for the SIGNER_PRIVATE_KEY:

ETHEREUM_NETWORK = "sepolia"
INFURA_API_KEY = "d23...x...6e"
SIGNER_PRIVATE_KEY = "0x561...x...61df"

5. Create send.js file​

In this example we'll create a JavaScript file (send.js) in the project directory which configures and sends the transaction.

const { Web3 } = require("web3");
const { ETH_DATA_FORMAT, DEFAULT_RETURN_FORMAT } = require("web3");
async function main() {
  // Configuring the connection to an Ethereum node
  const network = process.env.ETHEREUM_NETWORK;
  const web3 = new Web3(
    new Web3.providers.HttpProvider(
      `https://${network}.infura.io/v3/${process.env.INFURA_API_KEY}`,
    ),
  );
  // Creating a signing account from a private key
  const signer = web3.eth.accounts.privateKeyToAccount(
    process.env.SIGNER_PRIVATE_KEY,
  );
  web3.eth.accounts.wallet.add(signer);
  await web3.eth
    .estimateGas(
      {
        from: signer.address,
        to: "0xAED01C776d98303eE080D25A21f0a42D94a86D9c",
        value: web3.utils.toWei("0.0001", "ether"),
      },
      "latest",
      ETH_DATA_FORMAT,
    )
    .then((value) => {
      limit = value;
    });

  // Creating the transaction object
  const tx = {
    from: signer.address,
    to: "0xAED01C776d98303eE080D25A21f0a42D94a86D9c",
    value: web3.utils.toWei("0.0001", "ether"),
    gas: limit,
    nonce: await web3.eth.getTransactionCount(signer.address),
    maxPriorityFeePerGas: web3.utils.toWei("3", "gwei"),
    maxFeePerGas: web3.utils.toWei("3", "gwei"),
    chainId: 11155111,
    type: 0x2,
  };
  signedTx = await web3.eth.accounts.signTransaction(tx, signer.privateKey);
  console.log("Raw transaction data: " + signedTx.rawTransaction);
  // Sending the transaction to the network
  const receipt = await web3.eth
    .sendSignedTransaction(signedTx.rawTransaction)
    .once("transactionHash", (txhash) => {
      console.log(`Mining transaction ...`);
      console.log(`https://${network}.etherscan.io/tx/${txhash}`);
    });
  // The transaction is now on chain!
  console.log(`Mined in block ${receipt.blockNumber}`);
}
require("dotenv").config();
main();

6. Execute the transaction​

To execute the transaction, run:

node send.js

The terminal displays a log similar to the following. Click on the URL to view the transaction details.

Raw transaction data:
0x02f87383aa36a78084b2d05e0084b2d05e0082520894aed01c776d98303ee080d25a21f0a42d94a86d9c865af3107a400080c080a058b88e1e01517ecaab0349f838aa07cbc90297679b2bbf2f48fa6f53b02ae358a00564373fe50e923d87f1da8d7805533c71cf81af32d66b3b2f45e972e4896fde
Mining transaction ...
https://sepolia.etherscan.io/tx/0x31581c7ac2020de48d48363171fb3406f19fd14e67575695dafba51295959049
Mined in block 3773903