ERC-4337 Account Abstraction

Build and send UserOperations for smart contract wallets

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Build, sign, and send ERC-4337 UserOperations for smart contract wallets. Interact with bundlers and paymasters.

Why Account Abstraction?

Traditional EOA wallets have limitations:

• Single key = single point of failure
• Can’t batch transactions
• User pays gas in ETH only
• No account recovery

Smart contract wallets (ERC-4337) enable:

• Multi-sig, social recovery
• Batch transactions
• Sponsored gas (paymasters)
• Session keys, spending limits
• Any token for gas

Planned Implementation

Build UserOperation

import { UserOperation } from './UserOperation.js';

const userOp = await UserOperation.build({
  sender: smartWalletAddress,
  callData: encodeTransfer(recipient, amount),
  // Optional: use paymaster for sponsored gas
  paymaster: PAYMASTER_ADDRESS,
  // Signer for the smart wallet
  signer,
  // EntryPoint version
  entryPoint: ENTRYPOINT_V07,
});

// userOp is ready to send to bundler

Send to Bundler

import { Bundler } from './Bundler.js';

const bundler = Bundler('https://api.pimlico.io/v2/1/rpc?apikey=...');

// Send UserOperation
const userOpHash = await bundler.sendUserOperation(userOp);

// Wait for inclusion
const receipt = await bundler.waitForUserOperation(userOpHash);
console.log('Included in tx:', receipt.transactionHash);

Batch Transactions

// Execute multiple calls in one UserOperation
const userOp = await UserOperation.build({
  sender: smartWalletAddress,
  calls: [
    { to: USDC, data: encodeApprove(spender, amount) },
    { to: DEX, data: encodeSwap(USDC, WETH, amount) },
    { to: WETH, data: encodeWithdraw() },
  ],
  signer,
});

Paymaster (Sponsored Gas)

// User pays no gas - paymaster covers it
const userOp = await UserOperation.build({
  sender: smartWalletAddress,
  callData: encodeTransfer(recipient, amount),
  paymaster: {
    address: PAYMASTER_ADDRESS,
    // Get paymaster signature
    getData: async (partialUserOp) => {
      return await paymasterService.sign(partialUserOp);
    }
  },
  signer,
});

ERC-20 Gas Payment

// Pay gas in USDC instead of ETH
const userOp = await UserOperation.build({
  sender: smartWalletAddress,
  callData: encodeTransfer(recipient, amount),
  paymaster: {
    address: TOKEN_PAYMASTER,
    token: USDC_ADDRESS,
    // Paymaster will pull USDC from user for gas
  },
  signer,
});

Session Keys

// Create limited session key
const sessionKey = await SessionKey.create({
  wallet: smartWalletAddress,
  permissions: {
    // Only allow transfers to specific addresses
    allowedTargets: [FRIEND_ADDRESS],
    // Max 100 USDC per transaction
    maxAmount: parseUnits('100', 6),
    // Valid for 24 hours
    validUntil: Date.now() + 86400000,
  },
  mainSigner,
});

// Use session key (no main key needed)
const userOp = await UserOperation.build({
  sender: smartWalletAddress,
  callData: encodeTransfer(FRIEND_ADDRESS, parseUnits('50', 6)),
  signer: sessionKey,
});

Bundler Providers

Popular bundler services:

• Pimlico
• Alchemy
• Stackup
• Biconomy

// Pimlico
const bundler = Bundler('https://api.pimlico.io/v2/1/rpc?apikey=KEY');

// Alchemy
const bundler = Bundler('https://eth-mainnet.g.alchemy.com/v2/KEY');

// Self-hosted
const bundler = Bundler('http://localhost:3000/rpc');

Smart Wallet Factories

Support for popular smart wallet implementations:

// Safe (Gnosis)
import { SafeAccount } from './accounts/safe.js';

// Kernel (ZeroDev)
import { KernelAccount } from './accounts/kernel.js';

// SimpleAccount (reference impl)
import { SimpleAccount } from './accounts/simple.js';

Resources

• ERC-4337 Specification
• eth-infinitism/account-abstraction
• ERC-4337 Bundler Spec

Related

• ethers-signer — EOA signing
• permit — Gasless approvals
• multicall — Batch reads