Your first EVM Smart Contract

Your First Smart Contract

Overview

In this guide, we'll create, deploy, and interact with a simple smart contract on UOMI's EVM network using Hardhat. We'll build a basic "Counter" contract that can increment and retrieve a number.

Prerequisites

Before starting, ensure you have:

• Node.js installed

• A code editor (VS Code recommended)

• A MetaMask wallet with some test tokens

• Basic knowledge of Solidity

Project Setup

1. Create a new directory and initialize the project:

mkdir counter-contract
cd counter-contract
npm init -y

1. Install required dependencies:

npm install --save-dev hardhat @nomicfoundation/hardhat-toolbox

1. Create a Hardhat project:

npx hardhat init

Select "Create a JavaScript project" when prompted.

Writing the Contract

Create a new file contracts/Counter.sol:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

contract Counter {
    uint256 private count;
    
    // Event to emit when the counter changes
    event CountUpdated(uint256 newCount);
    
    constructor() {
        count = 0;
    }
    
    function increment() public {
        count += 1;
        emit CountUpdated(count);
    }
    
    function getCount() public view returns (uint256) {
        return count;
    }
}

Deployment Script

Create/modify scripts/deploy.js:

async function main() {
  const Counter = await ethers.getContractFactory("Counter");
  const counter = await Counter.deploy();
  await counter.waitForDeployment();

  console.log("Counter deployed to:", await counter.getAddress());
}

main()
  .then(() => process.exit(0))
  .catch((error) => {
    console.error(error);
    process.exit(1);
  });

Test the Contract

Create test/Counter.js:

const { expect } = require("chai");

describe("Counter", function () {
  let counter;

  beforeEach(async function () {
    const Counter = await ethers.getContractFactory("Counter");
    counter = await Counter.deploy();
  });

  it("Should start with count of 0", async function () {
    expect(await counter.getCount()).to.equal(0);
  });

  it("Should increment count", async function () {
    await counter.increment();
    expect(await counter.getCount()).to.equal(1);
  });
});

Run the tests:

npx hardhat test

Deploy to Testnet

1. Configure your network in hardhat.config.js:

require("@nomicfoundation/hardhat-toolbox");

// Go to https://finney.uomi.ai and replace this with your own RPC URL
const FINNEY_RPC_URL = "https://finney.uomi.ai";

// Replace this private key with your own
// To export your private key from Metamask, go to Account Details > Export Private Key
const PRIVATE_KEY = "YOUR-METAMASK-PRIVATE-KEY";

module.exports = {
  solidity: "0.8.19",
  networks: {
    finney: {
      url: FINNEY_RPC_URL,
      accounts: [PRIVATE_KEY],
    },
  },
};

1. Deploy to Finney testnet:

npx hardhat run scripts/deploy.js --network finney

Interact with Your Contract

After deployment, you can interact with your contract using:

1. The Hardhat console:

npx hardhat console --network finney

1. Example interactions:

// Get the contract
const Counter = await ethers.getContractFactory("Counter");
const counter = await Counter.attach("YOUR-DEPLOYED-CONTRACT-ADDRESS");

// Get the current count
const count = await counter.getCount();
console.log("Current count:", count);

// Increment the counter
await counter.increment();

Next Steps

Now that you've deployed your first contract, you can:

1. Add more functionality to your contract

2. Create a frontend to interact with it

3. Learn about contract security and best practices

4. Explore more complex smart contract patterns

Common Issues and Solutions

⚠️ Common Problems

• Transaction Failed: Make sure you have enough tokens for gas

• Contract Not Found: Verify the contract address is correct

• Network Issues: Ensure you're connected to the correct network

Resources

• Solidity Documentation

• Hardhat Documentation

• OpenZeppelin Contracts