Smart Contract Series

Smart Contract Deployment on Sepolia Testnet using Hardhat

How to deploy smart contract on Sepolia Testnet using hardhat

In this article context, we will be covering how we can deploy smart contract on Sepolia Testnet using hardhat configuration.

Sepolia Testnet

Sepolia is the latest testnet of Ethereum Blockchain. It is based on the Proof of Work(PoW) consensus mechanism.

Hardhat

Hardhat is a development environment where we can compile, run, deploy, debug and test our smart contracts.

Step 1: Add Sepolia Testnet to your Metamask and get some fake Sepolia Ethers

Sepolia Testnet

Step 2: Initialize the project

npm init

It will create a new package.json file which you can edit accordingly.

{  
 "name": "MySepoliaNFT",   
 "version": "1.0.0",  
 "description": "",  
 "main": "index.js",  
 "engines": {     
    "node": "12.19.0"    
  },  
 "scripts": {   
   "test": "echo \"Error: no test specified\" && exit 1", 
   "start": "nodemon index.js"
 },    
 "keywords": [],    
 "author": "",    
 "license": "ISC"
}

Step 3: Write smart contract

Create a folder contracts/ and create a new file called MySepolia.sol.

Make sure to install OpenZeppelin library as we are extending classes from OpenZeppelin Contracts library. npm install @openzeppelin/contracts.

Copy the following code to your smart contract file.

// SPDX-License-Identifier: MIT
pragma solidity >=0.8.0 <0.9.0;
import “@openzeppelin/contracts/token/ERC721/ERC721.sol”;
import “@openzeppelin/contracts/utils/Counters.sol”;
import “@openzeppelin/contracts/access/Ownable.sol”;
contract MySepolia is ERC721, Ownable {
 using Counters for Counters.Counter;
 Counters.Counter private _tokenIds;
 using Strings for uint256;
 
 mapping(uint256 => string) private _tokenURIs;
 string private _baseURIextended;
 constructor() ERC721(“MySepolia”, “MySepolia”) {}
 function setBaseURI(string memory baseURI_) external onlyOwner {
   _baseURIextended = baseURI_;
 }
 function _setTokenURI(uint256 tokenId, string memory _tokenURI)
 internal
 virtual
 {
   require(
    _exists(tokenId),
    “ERC721Metadata: URI set of nonexistent token”
   );
   _tokenURIs[tokenId] = _tokenURI;
 }
 function _baseURI() internal view virtual override returns (string memory) {
    return _baseURIextended;
 }
 function tokenURI(uint256 tokenId)
 public
 view
 virtual
 override
 returns (string memory)
 {
   require(
   _exists(tokenId),
   “ERC721Metadata: URI query for nonexistent token”
   );
   string memory _tokenURI = _tokenURIs[tokenId];
   string memory base = _baseURI();
   if (bytes(base).length == 0) {
     return _tokenURI;
   }
   if (bytes(_tokenURI).length > 0) {
     return string(abi.encodePacked(base, _tokenURI));
   }
   return string(abi.encodePacked(base, tokenId.toString()));
 }
 function mintNFT(address recipient, string memory _tokenURI)
 public onlyOwner
 returns (uint256)
 {
   _tokenIds.increment();
   uint256 newItemId = _tokenIds.current();
   _mint(recipient, newItemId);
   _setTokenURI(newItemId, _tokenURI);
   return newItemId;
 }
}

Step 4: Install Hardhat & Ethers.js

npm install --save-dev hardhat 
npm install --save-dev @nomiclabs/hardhat-ethers 'ethers@^5.0.0'

Step 5: Create Hardhat project

npx hardhat

You will get a prompt like below and select “create an empty hardhat.config.js”. It will create an empty hardhat.config.js file in your project folder.

888    888                      888 888               888
888    888                      888 888               888   
888    888                      888 888               888   
8888888888  8888b.  888d888 .d88888 88888b.   8888b.  888888
888    888     "88b 888P"  d88" 888 888 "88b     "88b 888   
888    888 .d888888 888    888  888 888  888 .d888888 888   
888    888 888  888 888    Y88b 888 888  888 888  888 Y88b. 
888    888 "Y888888 888     "Y88888 888  888 "Y888888  "Y888Welcome to Hardhat v2.8.0? What do you want to do? ...
  Create a basic sample project
  Create an advanced sample project
  Create an advanced sample project that uses TypeScript
> Create an empty hardhat.config.js
  Quit

Step 6: Update hardhat.config.js

/**
 * @type import(‘hardhat/config’).HardhatUserConfig
 */
require(“dotenv”).config();
require(“@nomiclabs/hardhat-ethers”);
const { API_URL, PRIVATE_KEY } = process.env;
module.exports = {
   solidity: "0.8.9",  
   defaultNetwork: "sepolia", 
   networks: {    
     hardhat: {},   
     sepolia: {     
      url: API_URL,      
      accounts: [`0x${PRIVATE_KEY}`],   
     }
   }
};

Make sure your .env file contains API_URL and PRIVATE_KEY. Your .env file should look like below:

API_URL = https://rpc.sepolia.online
PRIVATE_KEY = 'Metamask Private Key'
Other RPC URLs which can be used as API_URL
--------------------------
https://rpc.sepolia.dev
https://rpc.sepolia.online
https://www.sepoliarpc.space
https://rpc.sepolia.org
https://rpc-sepolia.rockx.com

Step 7: Compile smart contract

npx hardhat compile

Step 8: Write deploy script

Create another folder called scripts/ and create a new file called deploy.js and add the following content to it.

async function main() {  
  const MySepolia = await ethers.getContractFactory("MySepolia");     
  const MySepoliaContract = await MySepolia.deploy();
  console.log("Contract deployed to address:",      MySepoliaContract.address);
}
main().then(() => 
  process.exit(0)
).catch((error) => {        
   console.log(error);    
   process.exit(1);  
});

Step 9: Deploy smart contract

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

You will get a console output like below:

Contract deployed to address: 0xf4AF5af8BC0031E518Bba8cb31f69D160FfED6A9

Now you can verify the deployed contract address on sepolia block explorer. The transaction will look something like below:

Credit: Author

Great! You have successfully deployed your smart contract on Sepolia Testnet.

Happy DEPLOYing!

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