The builder interface is flexible enough to support any implementation of an ERC-4337 Smart Account. However, there are already a few common implementations used within the ecosystem already. Rather then create the same builder and middleware functions over and over again, we've shipped a few useful presets for commonly used implementations.

View the source code for Presets on GitHub.

📘

Preset for [insert favorite contract account] is not included?? :(

No worries! Userop.js is open for PRs. Alternatively, let us know what type of presets you'd like to see and we'll work together to get it shipped. 🤝

Builder

Builder presets are pre-configured builders over a known contract account implementation. Presets can be used as-is or modified with the get and set functions.

📘

Looking for a concrete example?

All builder presets are also used in the ERC-4337 examples repo. For each preset, you can find working code samples in the scripts directory.

SimpleAccount

The SimpleAccount preset is an abstraction to build User Operations for an ERC-4337 account based on SimpleAccount.sol.

import { Client, Presets } from "userop";

const simpleAccount = await Presets.Builder.SimpleAccount.init(
  signer, // Any object compatible with ethers.Signer
  config.rpcUrl
);
const client = await Client.init(config.rpcUrl);

const res = await client.sendUserOperation(
  simpleAccount.execute(target, value, "0x"),
  { onBuild: (op) => console.log("Signed UserOperation:", op) }
);
console.log(`UserOpHash: ${res.userOpHash}`);

console.log("Waiting for transaction...");
const ev = await res.wait();
console.log(`Transaction hash: ${ev?.transactionHash ?? null}`);

Kernel

The Kernel preset is an abstraction to build User Operations for an ERC-4337 account based on ZeroDev Kernel V2 - a modular contract account framework. It deploys with the ECDSA validator by default.

🚧

Only available on Polygon Mumbai

Kernel V2 factories and validators are currently only deployed on Polygon Mumbai.

import { Client, Presets } from "userop";

const kernel = await Presets.Builder.Kernel.init(
  signer, // Any object compatible with ethers.Signer
  config.rpcUrl,
);
const client = await Client.init(config.rpcUrl);

const res = await client.sendUserOperation(
  kernel.execute({to, value, data: "0x"}),
  { onBuild: (op) => console.log("Signed UserOperation:", op) }
);
console.log(`UserOpHash: ${res.userOpHash}`);

console.log("Waiting for transaction...");
const ev = await res.wait();
console.log(`Transaction hash: ${ev?.transactionHash ?? null}`);

Middleware

Middleware presets are common implementations of middleware functions that can be re-used for different builder instances.

View middleware functions on GitHub.

estimateUserOperationGas

A middleware function for sending UserOperations to the eth_estimateUserOperationGas endpoint in order to estimate reasonable gas limits for preVerificationGas, verificationGasLimit, and callGasLimit.

import { Presets } from "userop";

// provider is an ethers.js JSON-RPC provider.
builder = builder.useMiddleware(Presets.Middleware.estimateUserOperationGas(provider))

getGasPrice

A middleware function for getting the latest values for maxFeePerGas and maxPriorityFeePerGas.

import { Presets } from "userop";

// provider is an ethers.js JSON-RPC provider.
builder = builder.useMiddleware(Presets.Middleware.getGasPrice(provider))

verifyingPaymaster

A middleware function for requesting gas sponsorship from a Paymaster service. The middleware assumes that the service implements this proposed JSON-RPC API for verifying paymasters.

import { Presets } from "userop";

builder = builder.useMiddleware(
  Presets.Middleware.verifyingPaymaster(paymasterRpc, paymasterCtx)
)

EOASignature

A middleware function for signing the User Operation with an EOA private key.

import { ethers } from "ethers";
import { Presets } from "userop";

// signer is an ethers.js Wallet instance.
const signer = new ethers.Wallet(signingKey);
builder = builder.useMiddleware(Presets.Middleware.EOASignature(signer))