FHEVM React Template

The FHEVM React Template is an ultra-minimal React project for building and running an FHEVM-enabled dApp. It works alongside the fhevm-hardhat-template and provides a simple development frontend for interacting with the FHECounter.sol contract.

This template also illustrates how to run your FHEVM-dApp on both Sepolia as well as a local Hardhat Node (much faster).

Features

• @zama-fhe/relayer-sdk: Fully Homomorphic Encryption for Ethereum Virtual Machine
• React: Modern UI framework for building interactive interfaces
• Next.js: Next-generation frontend build tool
• Tailwind: Utility-first CSS framework for rapid UI development

Requirements

• You need to have Metamask browser extension installed on your browser.

Local Hardhat Network (to add in MetaMask)

Follow the step-by-step guide in the Hardhat + MetaMask documentation to set up your local devnet using Hardhat and MetaMask.

• Name: Hardhat
• RPC URL: http://127.0.0.1:8545
• Chain ID: 31337
• Currency symbol: ETH

Install

1. Clone this repository.
2. From the repo root, run:

npm install

Quickstart

1. Setup your hardhat environment variables:

Follow the detailed instructions in the FHEVM documentation to setup MNEMONIC + INFURA_API_KEY Hardhat environment variables

2. Start a local Hardhat node (new terminal):

# Default RPC: http://127.0.0.1:8545  | chainId: 31337
npm run hardhat-node

3. Launch the frontend in mock mode:

npm run dev:mock

4. Start your browser with the Metamask extension installed and open http://localhost:3000

5. Open the Metamask extension to connect to the local Hardhat node i. Select Add network. ii. Select Add a network manually. iii. Enter your Hardhat Network RPC URL, http://127.0.0.1:8545 (or http://localhost:8545). iv. Enter your Hardhat Network chain ID, 31337 (or 0x539 in hexadecimal format).

Run on Sepolia

1. Deploy your contract on Sepolia Testnet

npm run deploy:sepolia

2. In your browser open http://localhost:3000

3. Open the Metamask extension to connect to the Sepolia network

How to fix Hardhat Node + Metamask Errors ?

When using MetaMask as a wallet provider with a development node like Hardhat, you may encounter two common types of errors:

1. ⚠️ Nonce Mismatch ❌💥

MetaMask tracks wallet nonces (the number of transactions sent from a wallet). However, if you restart your Hardhat node, the nonce is reset on the dev node, but MetaMask does not update its internal nonce tracking. This discrepancy causes a nonce mismatch error.

2. ⚠️ View Function Call Result Mismatch ❌💥

MetaMask caches the results of view function calls. If you restart your Hardhat node, MetaMask may return outdated cached data corresponding to a previous instance of the node, leading to incorrect results.

✅ How to Fix Nonce Mismatch:

To fix the nonce mismatch error, simply clear the MetaMask cache:

1. Open the MetaMask browser extension.
2. Select the Hardhat network.
3. Go to Settings > Advanced.
4. Click the "Clear Activity Tab" red button to reset the nonce tracking.

The correct way to do this is also explained here.

✅ How to Fix View Function Return Value Mismatch:

To fix the view function result mismatch:

1. Restart the entire browser. MetaMask stores its cache in the extension's memory, which cannot be cleared by simply clearing the browser cache or using MetaMask's built-in cache cleaning options.

By following these steps, you can ensure that MetaMask syncs correctly with your Hardhat node and avoid potential issues related to nonces and cached view function results.

Project Structure Overview

Key Files/Folders

• <root>/packages/site/fhevm: This folder contains the essential hooks needed to interact with FHEVM-enabled smart contracts. It is meant to be easily copied and integrated into any FHEVM + React project.

• <root>/packages/site/hooks/useFHECounter.tsx: A simple React custom hook that demonstrates how to use the useFhevm hook in a basic use case, serving as an example of integration.

Secondary Files/Folders

• <root>/packages/site/hooks/metamask: This folder includes hooks designed to manage the MetaMask Wallet provider. These hooks can be easily adapted or replaced to support other wallet providers, following the EIP-6963 standard,
• Additionally, the project is designed to be flexible, allowing developers to easily replace ethers.js with a more React-friendly library of their choice, such as Wagmi.

Documentation

• Hardhat + MetaMask: Set up your local devnet step by step using Hardhat and MetaMask.
• FHEVM Documentation
• FHEVM Hardhat
• @zama-fhe/relayer-sdk Documentation
• Setting up MNEMONIC and INFURA_API_KEY
• React Documentation
• FHEVM Discord Community
• GitHub Issues

License

This project is licensed under the BSD-3-Clause-Clear License - see the LICENSE file for details.