Version: SDK V3

Creating Gasless Transactions ⛽️

Here, we'll guide you through a Node.js script in TypeScript to mint NFTs without any gas fees on the Polygon Amoy.

Prerequisites

Before you dive in, please make sure you've covered Environment Setup and Account Initialization. We'll be using the NFT contract here. Contract Address: 0x1758f42Af7026fBbB559Dc60EcE0De3ef81f665e.

🔄 Updated Imports for Gasless NFT Transactions

We've added new imports to our existing setup for gasless NFT minting:

ethers: Essential for specific Ethereum contract functions, such as encoding NFT minting data.
PaymasterMode: This defines how the Paymaster handles gas fees, enabling gasless transactions by setting it to SPONSORED.

// Import necessary modules and configurations
import { config } from "dotenv"; // dotenv for loading environment variables from a .env file
import { IBundler, Bundler } from "@biconomy/bundler"; // Biconomy bundler for managing gasless transactions
import {
  DEFAULT_ENTRYPOINT_ADDRESS,
  BiconomySmartAccountV2,
} from "@biconomy/account"; // Default entry point and smart account module from Biconomy
import { Wallet, ethers, providers } from "ethers"; // ethers for interacting with the Ethereum blockchain
import {
  IPaymaster,
  BiconomyPaymaster,
  PaymasterMode,
} from "@biconomy/paymaster"; // Paymaster interface and Biconomy implementation
import {
  ECDSAOwnershipValidationModule,
  DEFAULT_ECDSA_OWNERSHIP_MODULE,
} from "@biconomy/modules"; // Modules for ownership validation

config(); // Load environment variables from .env file

🛠 Building the NFT Mint Function

We'll build the mintNFT function in a step-by-step manner for clarity.

Step 1: Initialize the Smart Account

async function mintNFT() {
  // Create and initialize the smart account
  const smartAccount = await createSmartAccount();
  // Retrieve the address of the initialized smart account
  const address = await smartAccount.getAccountAddress();
  // ...[continuing the function]...
}

createSmartAccount(): This custom function creates and initializes your Smart Account.
getAccountAddress(): Retrieves the address of your newly minted Smart Account.

Step 2: Create the NFT Contract Interface

// Define the interface for interacting with the NFT contract
const nftInterface = new ethers.utils.Interface([
  "function safeMint(address _to)",
]);

Interface from ethers: This utility helps us interact with our NFT contract.

Step 3: Encode Function Data

// Encode the data for the 'safeMint' function call with the smart account address
const data = nftInterface.encodeFunctionData("safeMint", [address]);

encodeFunctionData: Packs your function call into a transaction, targeting the safeMint function.

🧱 Constructing the UserOp

Now, let's assemble the User Operation (UserOp) for our gasless transaction:

Step 1: Declare Contract Address and Build Transaction

// Specify the address of the NFT contract
const nftAddress = "0x1758f42Af7026fBbB559Dc60EcE0De3ef81f665e";

// Define the transaction to be sent to the NFT contract
const transaction = {
  to: nftAddress,
  data: data,
};

Contract Address: Where our NFT lives.
Transaction: The action we're preparing to execute.

Step 2: Construct the Partial UserOp

// Build a partial User Operation (UserOp) with the transaction and set it to be sponsored
let partialUserOp = await smartAccount.buildUserOp([transaction], {
  paymasterServiceData: {
    mode: PaymasterMode.SPONSORED,
  },
});

buildUserOp: Prepares our UserOp with the required transaction details.
PaymasterMode.SPONSORED: Ensures our transaction is gasless!

🌟 Execute the UserOp with Paymaster

Time to mint that NFT! 🖼️

// Try to execute the UserOp and handle any errors
try {
  // Send the UserOp through the smart account
  const userOpResponse = await smartAccount.sendUserOp(partialUserOp);
  // Wait for the transaction to complete and retrieve details
  const transactionDetails = await userOpResponse.wait();
  // Log the transaction details URL and the URL to view minted NFTs
  console.log(`View Minted NFTs: https://testnets.opensea.io/${address}`);
  console.log(
    `Transaction Details: https://www.oklink.com/amoy/tx/${transactionDetails.receipt.transactionHash}`,
  );
} catch (e) {
  // Log any errors encountered during the transaction
  console.log("Error encountered: ", e);
}

sendUserOp: Sends our prepared UserOp.
wait: Awaits the transaction confirmation.
Result: Outputs links to view the transaction and the minted NFT.

📝 Click to view the complete mintNFT function

And that's it! You've successfully executed a gasless NFT minting transaction. 🚀💡

// Function to mint an NFT gaslessly
async function mintNFT() {
  // Create and initialize the smart account
  const smartAccount = await createSmartAccount();
  // Retrieve the address of the initialized smart account
  const address = await smartAccount.getAccountAddress();

  // Define the interface for interacting with the NFT contract
  const nftInterface = new ethers.utils.Interface([
    "function safeMint(address _to)",
  ]);

  // Encode the data for the 'safeMint' function call with the smart account address
  const data = nftInterface.encodeFunctionData("safeMint", [address]);

  // Specify the address of the NFT contract
  const nftAddress = "0x1758f42Af7026fBbB559Dc60EcE0De3ef81f665e";

  // Define the transaction to be sent to the NFT contract
  const transaction = {
    to: nftAddress,
    data: data,
  };

  // Build a partial User Operation (UserOp) with the transaction and set it to be sponsored
  let partialUserOp = await smartAccount.buildUserOp([transaction], {
    paymasterServiceData: {
      mode: PaymasterMode.SPONSORED,
    },
  });

  // Try to execute the UserOp and handle any errors
  try {
    // Send the UserOp through the smart account
    const userOpResponse = await smartAccount.sendUserOp(partialUserOp);
    // Wait for the transaction to complete and retrieve details
    const transactionDetails = await userOpResponse.wait();
    // Log the transaction details URL and the URL to view minted NFTs
    console.log(
      `Transaction Details: https://www.oklink.com/amoy/tx/${transactionDetails.receipt.transactionHash}`,
    );
    console.log(`View Minted NFTs: https://testnets.opensea.io/${address}`);
  } catch (e) {
    // Log any errors encountered during the transaction
    console.log("Error encountered: ", e);
  }
}

And that's it! You've successfully executed a gasless NFT minting transaction. 🚀💡

📝 Click to view the complete

// Import necessary modules and configurations
import { config } from "dotenv"; // dotenv for loading environment variables from a .env file
import { IBundler, Bundler } from "@biconomy/bundler"; // Biconomy bundler for managing gasless transactions
import {
  DEFAULT_ENTRYPOINT_ADDRESS,
  BiconomySmartAccountV2,
} from "@biconomy/account"; // Default entry point and smart account module from Biconomy
import { Wallet, ethers, providers } from "ethers"; // ethers for interacting with the Ethereum blockchain
import {
  IPaymaster,
  BiconomyPaymaster,
  PaymasterMode,
} from "@biconomy/paymaster"; // Paymaster interface and Biconomy implementation
import {
  ECDSAOwnershipValidationModule,
  DEFAULT_ECDSA_OWNERSHIP_MODULE,
} from "@biconomy/modules"; // Modules for ownership validation

config(); // Load environment variables from .env file

// Set up the Ethereum provider and wallet
const provider = new providers.JsonRpcProvider(
  "https://rpc-amoy.polygon.technology/", // JSON-RPC provider URL for the Polygon Amoy test network
);

const wallet = new Wallet(process.env.PRIVATE_KEY || "", provider); // Creating a wallet instance with a private key from environment variables

// Configure the Biconomy Bundler
const bundler: IBundler = new Bundler({
  bundlerUrl:
    "https://bundler.biconomy.io/api/v2/80002/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44", // URL to the Biconomy bundler service

  chainId: 80002, // Chain ID for Polygon Amoy test network

  entryPointAddress: DEFAULT_ENTRYPOINT_ADDRESS, // Default entry point address for the bundler
});

// Configure the Paymaster
const paymaster: IPaymaster = new BiconomyPaymaster({
  paymasterUrl:
    "https://paymaster.biconomy.io/api/v1/2/Tpk8nuCUd.70bd3a7f-a368-4e5a-af14-80c7f1fcda1a", // URL to the Biconomy paymaster service
});

// Function to create a module for ownership validation
async function createModule() {
  return await ECDSAOwnershipValidationModule.create({
    signer: wallet, // The wallet acting as the signer
    moduleAddress: DEFAULT_ECDSA_OWNERSHIP_MODULE, // Address of the default ECDSA ownership validation module
  });
}

// Function to create a Biconomy Smart Account
async function createSmartAccount() {
  const module = await createModule(); // Create the validation module

  let smartAccount = await BiconomySmartAccountV2.create({
    chainId: 80002, // Chain ID for the Polygon Amoy network
    bundler: bundler, // The configured bundler instance
    paymaster: paymaster, // The configured paymaster instance
    entryPointAddress: DEFAULT_ENTRYPOINT_ADDRESS, // Default entry point address
    defaultValidationModule: module, // The default validation module
    activeValidationModule: module, // The active validation module
  });

  console.log(
    "Smart Account Address: ",
    await smartAccount.getAccountAddress(), // Logging the address of the created smart account
  );

  return smartAccount;
}

// Function to mint an NFT gaslessly
async function mintNFT() {
  // Create and initialize the smart account
  const smartAccount = await createSmartAccount();
  // Retrieve the address of the initialized smart account
  const address = await smartAccount.getAccountAddress();

  // Define the interface for interacting with the NFT contract
  const nftInterface = new ethers.utils.Interface([
    "function safeMint(address _to)",
  ]);

  // Encode the data for the 'safeMint' function call with the smart account address
  const data = nftInterface.encodeFunctionData("safeMint", [address]);

  // Specify the address of the NFT contract
  const nftAddress = "0x1758f42Af7026fBbB559Dc60EcE0De3ef81f665e";

  // Define the transaction to be sent to the NFT contract
  const transaction = {
    to: nftAddress,
    data: data,
  };

  // Build a partial User Operation (UserOp) with the transaction and set it to be sponsored
  let partialUserOp = await smartAccount.buildUserOp([transaction], {
    paymasterServiceData: {
      mode: PaymasterMode.SPONSORED,
    },
  });

  // Try to execute the UserOp and handle any errors
  try {
    // Send the UserOp through the smart account
    const userOpResponse = await smartAccount.sendUserOp(partialUserOp);
    // Wait for the transaction to complete and retrieve details
    const transactionDetails = await userOpResponse.wait();
    // Log the transaction details URL and the URL to view minted NFTs
    console.log(
      `Transaction Details: https://www.oklink.com/amoy/tx/${transactionDetails.receipt.transactionHash}`,
    );
    console.log(`View Minted NFTs: https://testnets.opensea.io/${address}`);
  } catch (e) {
    // Log any errors encountered during the transaction
    console.log("Error encountered: ", e);
  }
}

mintNFT(); // Call mintNFT function

Creating Gasless Transactions ⛽️

🔄 Updated Imports for Gasless NFT Transactions​

🛠 Building the NFT Mint Function​

Step 1: Initialize the Smart Account​

Step 2: Create the NFT Contract Interface​

Step 3: Encode Function Data​

🧱 Constructing the UserOp​

Step 1: Declare Contract Address and Build Transaction​

Step 2: Construct the Partial UserOp​

🌟 Execute the UserOp with Paymaster​