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Version: SDK V4 (latest)

Send parallel user ops using 2D nonce

Overview​

This tutorial demonstrates how to send parallel user operations using 2D nonces.

What is a 2D Nonce? A 2D nonce is used in smart accounts to manage transaction ordering and parallel execution. Unlike traditional EOAs (Externally Owned Accounts) where nonces are strictly sequential (1, 2, 3, ...), smart accounts use a two-dimensional nonce composed of a "nonce key" and a "nonce value." This allows for more complex transaction dependencies and parallel processing.

As long as one user operation is not dependent on another, it can be sent in parallel.

For example, having a look at this user action flow:

  • Swap 100 USDC to DAI (tx 1)
  • Swap 100 DAI to USDT (tx 2)
  • Swap 1 WETH to USDT (tx 3)

We can see that tx 1 and 2 are dependent, these two cannot be executed in parallel but tx 3 can, as it is not dependent on the others

Prerequisites​

Step 1: Generate the config and Create Biconomy Smart Account​

import { createWalletClient } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { polygonAmoy } from "viem/chains";
import { createSmartAccountClient, UserOpResponse } from "@biconomy/account";

// Your configuration with private key and Biconomy API key
const config = {
  privateKey: "your-private-key",
  bundlerUrl: "", // <-- Read about this at https://legacy-docs.biconomy.io/dashboard#bundler-url
};

// Generate EOA from private key using ethers.js
const account = privateKeyToAccount("0x" + config.privateKey);
const signer = createWalletClient({
  account,
  chain: polygonAmoy,
  transport: http(),
});

// Create Biconomy Smart Account instance
const smartWallet = await createSmartAccountClient({
  signer,
  bundlerUrl: config.bundlerUrl,
});

const saAddress = await smartWallet.getAccountAddress();
console.log("SA Address", saAddress);

Get your signer from either ethers.js or viem and create a Biconomy Smart Account instance.

Step 2: Generate Transaction Data​

const toAddress = "0xaddress"; // Replace with the recipient's address
const transactionData = "0x123"; // Replace with the actual transaction data

// Build the transaction
const tx = {
  to: toAddress,
  data: transactionData,
};

Specify the recipient's address and transaction data to build the simple transaction.

Step 3: Send the parallel user operations​

// Send the transaction and get the transaction hash
const numberOfUserOpsToSend = 3;
const txPromises: Promise<UserOpResponse>[] = [];
for (let key = 1; key <= numberOfUserOpsToSend; key++) {
  // wrap the tx in a user op and send it
  // we don't want to await for the user op to be executed because we want to send all users ops at the same time
  const txPromise = smartAccount.sendTransaction([tx], {nonceOptions: {nonceKey: key});
  // save the promise response for later
  txPromises.push(txPromise);
}

// later we can resolve the promises to get user operation receipts
const userOpResponses: UserOpResponse[] = await Promise.all(txPromises);
userOpResponses.forEach(async (userOpResponse) => {
  const { wait } = userOpResponse;
  const receipt = await wait();
  console.log("Receipt: ", receipt);
})
caution
  • make sure your nonceKey is bigger than 0, a 0 nonceKey value will not use 2D nonces
  • make sure your transactions are not dependent one on another
  • make sure you do not await for each user operation to be executed, otherwise it will defeat the purpose of 2D nonces, causing sequential execution

That's it! You've successfully sent 3 parallel user ops using ethers.js/viem and the Biconomy Smart Account. Feel free to customize this example based on your specific use case.

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