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Send a transaction with Polygon

As with Ethereum, transactions are state-changing actions on the Polygon PoS blockchain. Examples of transactions are:

  • Regular transactions from one account to another.
  • Contract deployment transactions, or calling a function in a smart contract.

This tutorial uses the Ethereum Web3 JavaScript library to send a transaction between two accounts on the Polygon-Mumbai testnet.

Prerequisites​

info

You can use MetaMask or a similar Ethereum wallet to create an account for testing purposes on the Polygon blockchain.

Steps​

1. Add Polygon network to MetaMask​

Refer to the Polygon instructions to add the Polygon networks to MetaMask. This tutorial uses the Polygon Mumbai network.

2. Fund your account​

Use the Polygon faucet to load testnet MATIC on your account for the Mumbai network.

3. 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

4. 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

5. Create the .env file​

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

POLYGON_NETWORK = "polygon-mumbai"
INFURA_API_KEY = "<API-Key>"
SIGNER_PRIVATE_KEY = "<Private-Key>"

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

danger

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

6. 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.

send.js
const { Web3 } = require("web3");

async function main() {
  // Configuring the connection to the Polygon node
  const network = process.env.POLYGON_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);
  // Creating the transaction object
  const tx = {
    from: signer.address,
    to: "0xAED01C776d98303eE080D25A21f0a42D94a86D9c",
    value: web3.utils.toWei("0.001", "ether"),
  };
  // Assigning the right amount of gas
  tx.gas = await web3.eth.estimateGas(tx);

  // Sending the transaction to the network
  const receipt = await web3.eth
    .sendTransaction(tx)
    .once("transactionHash", (txhash) => {
      console.log(`Mining transaction ...`);
      console.log(`Transaction hash: ${txhash}`);
    });
  // The transaction is now on chain!
  console.log(`Mined in block ${receipt.blockNumber}`);
}

require("dotenv").config();
main();

7. Execute the transaction​

To execute the transaction, run:

node send.js

The command line will display the block number containing the transaction details.

8. View the transaction details​

Copy transaction hash and view the transaction in the Polygon Mumbai block explorer.

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