In this article we are going to create a smart contract to mint an NFT on Ethereum.
Setup the project
To start the project we will use the hardhat that will provide us with a boilerplate to deploy the contract, do tests, etc.
Installing the hardhat
We will install hardhat as development dependency using the yarn.
Open a new terminal and run these commands:
mkdir nft-token
cd nft-token
yarn init -y
yarn add hardhat -D
In the same directory where you installed Hardhat run:
npx hardhat
Select Create an empty hardhat.config.js with your keyboard and hit enter.
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❯ Create an empty hardhat.config.js
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Creating the files and directories
Let's start by creating a directory called contracts in the root folder.
/node_modules
/contracts
hardhat.config.js
package.json
yarn.lock
After creating the folder we can create our first file of our contract inside the directory, let's call it: factoryNFT.sol
/node_modules
/contracts
| - factoryNFT.sol
hardhat.config.js
package.json
yarn.lock
Writing the smart contract
Now we go to the most anticipated part of the article, writing our contract.
Note: You can review the basics in my other article: How to create a smart contract to receive donations using Solidity
Let's start defining the pragma version:
factoryNFT.sol
pragma solidity ^0.8.3;
To help us, we will install the openzeppelin contracts package.
yarn add @openzeppelin/contracts @openzeppelin/hardhat-upgrades
Now we can import it into the contract.
factoryNFT.sol
pragma solidity ^0.8.3;
import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
We made 3 imports:
Counters: is a useful one that will help us increment a tokenId for each new token.
ERC721URIStorage: we will provide some functions to handle our tokenURI, which contains metadata and image.
ERC721: will we provide some basic functions of the ERC721;
Inheriting the OpenZeppelin contract
Now we can start by defining the name of our contract and inheriting the OpenZeppelin contracts.
factoryNFT.sol
pragma solidity ^0.8.3;
import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
contract FactoryNFT is ERC721URIStorage {
using Counters for Counters.Counter;
Counters.Counter private _tokenIds;
constructor() ERC721("Factory NFT", "FTN") {
}
}
Creating our Mint function
Let's start by creating our function calling createToken, where it will receive as a parameter, our tokenURI.
factoryNFT.sol
pragma solidity ^0.8.3;
import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
contract FactoryNFT is ERC721URIStorage {
using Counters for Counters.Counter;
Counters.Counter private _tokenIds;
constructor() ERC721("Factory NFT", "FTN") {
}
function createToken(string memory tokenURI) public returns (uint) {
}
}
Now let's increment the amount of token in storage and save it in a variable.
factoryNFT.sol
pragma solidity ^0.8.3;
import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
contract FactoryNFT is ERC721URIStorage {
using Counters for Counters.Counter;
Counters.Counter private _tokenIds;
constructor() ERC721("Factory NFT", "FTN") {
}
function createToken(string memory tokenURI) public returns (uint) {
_tokenIds.increment();
uint256 newItemId = _tokenIds.current();
}
}
Now we can put the main function of the contract which is to mint our NFT and set its tokenURI.
factoryNFT.sol
pragma solidity ^0.8.3;
import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
contract FactoryNFT is ERC721URIStorage {
using Counters for Counters.Counter;
Counters.Counter private _tokenIds;
constructor() ERC721("Factory NFT", "FTN") {
}
function createToken(string memory tokenURI) public returns (uint) {
_tokenIds.increment();
uint256 newItemId = _tokenIds.current();
_mint(msg.sender, newItemId);
_setTokenURI(newItemId, tokenURI);
return newItemId;
}
}
Compiling and testing the Contract
Now to test the contract, we are going to compile it and write a test for it.
First of all let's go to the hardhat.config.js
file and change the solidity version to ^0.8.3.
hardhat.config.js
/**
* @type import('hardhat/config').HardhatUserConfig
*/
module.exports = {
solidity: "^0.8.3",
};
Plugins
Now to test our contract we need to install some plugins for hardhat to help us interact with Ethereum and test our contracts.
yarn add -D @nomiclabs/hardhat-ethers ethers @nomiclabs/hardhat-waffle ethereum-waffle chai
After adding the plugins we need to add a line in hardhat.config.js
to setup the plugins.
hardhat.config.js
require("@nomiclabs/hardhat-waffle");
/**
* @type import('hardhat/config').HardhatUserConfig
*/
module.exports = {
solidity: "^0.8.3",
};
Writing the test
Now create a directory called test in the root folder and add called: factoryNFT.js
/node_modules
/contracts
/test
|- factoryNFT.js
hardhat.config.js
package.json
yarn.lock
Now I am going to put the test below and explain each line to understand it.
const { expect } = require("chai");
describe("Minting the token and returning it", function () {
it("should the contract be able to mint a function and return it", async function () {
const metadata = "https://opensea-creatures-api.herokuapp.com/api/creature/1" //Random metadata url
const FactoryContract = await ethers.getContractFactory("FactoryNFT"); // Getting the contract
const factoryContract = await FactoryContract.deploy(); //Deploying the Contract
const transaction = await factoryContract.createToken(metadata); // Minting the token
const tx = await transaction.wait() // Waiting for the token to be minted
const event = tx.events[0];
const value = event.args[2];
const tokenId = value.toNumber(); // Getting the tokenID
const tokenURI = await factoryContract.tokenURI(tokenId) // Using the tokenURI from ERC721 to retrieve de metadata
expect(tokenURI).to.be.equal(metadata); // Comparing and testing
});
});
Now let's configure the package.json to run our script, add this script to your package.json to compile the contract.
"scripts": {
"compile": "yarn hardhat compile"
}
package.json
{
"name": "hardhat",
"version": "1.0.0",
"main": "index.js",
"license": "MIT",
"scripts": {
"compile": "yarn hardhat compile"
},
"devDependencies": {
"@nomiclabs/hardhat-ethers": "^2.0.2",
"@nomiclabs/hardhat-waffle": "^2.0.1",
"chai": "^4.3.4",
"ethereum-waffle": "^3.4.0",
"ethers": "^5.4.6",
"hardhat": "^2.6.4"
},
"dependencies": {
"@openzeppelin/contracts": "^4.3.2",
"@openzeppelin/hardhat-upgrades": "^1.10.0"
}
}
Now just compile and run the test and we will have the result!.
yarn compile
npx hardhat test
So we come to the end and you can see my next article on how to deploy to rinkeby testnet How to deploy smart contract to Rinkeby Testnet using Infura and Hardhat.
Repository: https://github.com/EmanuelCampos/mint-nft
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Top comments (2)
Can this be done on a Chromebook?
When I try to input the terminal commands i get Unknown Command error.
Why is node modules not found when I do /node_modules? Do I have to install anything extra for it to work?