How to create an on-chain NFT game

Discover how to create your own NFT game using Avalanche
1.5 hours
Written by Viral Sangani


In this tutorial, we will learn how to create an NFT game with a Solidity smart contract deployed on Avalanche Network and a NextJS front-end to interact with the game.
We will be creating an Avengers-themed NFT game with an ERC20 token, which can be used to mint characters in the game and buy special powers from the marketplace. Yes, we will be creating a marketplace where players can buy additional powers for their character. The game will have the following features -
  • Each user can mint a character of their choice using the EPIC token.
  • One can get the EPIC tokens from the faucet we will be creating in the dApp.
  • Once the user has a character, they can enter the fight arena to fight against the boss (Thanos).
  • Each character will have Health Points(HP), Damage Points, and Attack Modes (Kick, Punch, etc...).
  • Users can buy special attacks from the marketplace for their character using EPIC tokens.
  • Each time a character hits the boss, the boss hits back and reduces the HP of the player.
  • Users can claim more health over time using EPIC tokens.
  • If a character's health reaches 0, they cannot play the game until they claim new health.
  • Boss will have very high HP, but boss's HP does not increase over time.
  • The boss character will be the same for all the players with the same HP and everyone has to collectively try to defeat the boss.
Sounds interesting? This is what the game we will be creating looks like:
NFT Game Demo


To successfully follow along with this tutorial, you will need a good understanding of ERC721 standards, Solidity language, the Hardhat framework, and the Next.js framework.
We will be using ethers.js library to interact with the smart contract and Next.js for the frontend.


  • Hardhat - Hardhat provides a local development environment for creating and testing blockchain applications.
  • Metamask - You will need a Metamask wallet installed in your browser.
  • Next.js - A web framework to create a user interface.
  • Arweave - We will store images related to a proposal on Arweave.
  • TailwindCSS - A CSS utility framework.

Project Setup

We will be using nextjs-hardhat-tailwind-starter to get the initial setup. Run the following code to get started with boilerplate code.
git clone mv nextjs-hardhat-tailwind-starter epic-nft-game cd epic-nft-game
This starter kit comes with all the packages you will need to get started with a dApp. You can see the list of the package in the starter kit here.
We will need a few more packages to create awesome UI for our game. Run the following code to add additional packages.
yarn add @headlessui/react dotenv react-lottie react-spring react-step-progress-bar react-toastify react-tooltip

Creating EPIC ERC20 Token

Rename contracts/ERC20Token.sol to EPICToken.sol and paste the following code.
// SPDX-License-Identifier: UNLICENSED pragma solidity ^0.8.0; import "@openzeppelin/contracts/token/ERC20/ERC20.sol"; contract EPICToken is ERC20 { constructor(string memory name, string memory symbol) ERC20(name, symbol) { _mint(msg.sender, 100000 * (10**18)); } function faucet(address recipient, uint256 amount) external { require(amount <= 20 ether, "Amount must be less than 20 ether"); _mint(recipient, amount); } }
In the EPICToken contract, we will accept the token name and token symbol from the constructor and mint some tokens for the contract owner.
We also have a faucet method that will airdrop up to 20 EPIC tokens in the caller's account. Note that the method call will revert if more than 20 tokens are requested.

Creating NFTEpicGame smart contract

Create a file called NFTEpicGame.sol in the contracts folder and write the following code -
I know it's a lot to take in, let's go ahead and see what's happening in the smart contract.
import "@openzeppelin/contracts/token/ERC721/ERC721.sol"; import "@openzeppelin/contracts/token/ERC20/IERC20.sol"; import "@openzeppelin/contracts/utils/Counters.sol"; import "@openzeppelin/contracts/utils/math/SafeMath.sol"; import "@openzeppelin/contracts/utils/Strings.sol"; import "@openzeppelin/contracts/access/Ownable.sol"; import "@openzeppelin/contracts/security/ReentrancyGuard.sol"; import "./libraries/Base64.sol"; import "hardhat/console.sol";
Here we are importing all the necessary Openzeppelin contracts. We need ERC721 to mint character NFTs and IERC20 to call ERC20 methods on our EPIC token. We will be using some utility contracts like Counters.sol, SafeMath.sol, Strings.sol, Ownable.sol, ReentrancyGuard.sol and Base64.sol.
console.sol is provided by hardhat, used to add some debug statements in the smart contract which will be removed when the contract is compiled for deployment.
contract NFTEpicGame is ERC721, ReentrancyGuard, Ownable { using Counters for Counters.Counter; using SafeMath for uint256; Counters.Counter private _tokenIds; address epicToken; uint256 regenTime = 60; }
We will inherit from ERC721, ReentrancyGuard, and Ownable contract in our NFTEpicGame. ERC721 is used to mint NFT characters for our users. ReentrancyGuard is a modifier that can prevent reentrancy during certain functions (read more about ReentrancyGuard here). Ownable provides a basic access control mechanism where an owner account can be granted exclusive access to specific functions.
_tokenIds is used to keep track of all NFTs, epicToken is the contract address of our ERC20 token, and regenTime is the time in seconds user have to wait to reclaim the health (briefly explained below).
struct CharacterAttributes { uint256 characterIndex; string name; string imageURI; uint256 hp; uint256 maxHp; uint256[] attacks; uint256[] specialAttacks; uint256 lastRegenTime; } struct AttackType { uint256 attackIndex; string attackName; uint256 attackDamage; string attackImage; } struct SpecialAttackType { uint256 price; uint256 specialAttackIndex; string specialAttackName; uint256 specialAttackDamage; string specialAttackImage; } AttackType[] allAttacks; SpecialAttackType[] allSpecialAttacks; struct BigBoss { string name; string imageURI; uint256 hp; uint256 maxHp; uint256 attackDamage; } BigBoss public bigBoss; CharacterAttributes[] defaultCharacters; mapping(uint256 => CharacterAttributes) public nftHolderAttributes; mapping(address => uint256) public nftHolders;
  • CharacterAttributes struct is used to store all the character attributes of a player. An instance of CharacterAttributes is created when the user mints the character for the first time.
  • CharacterAttributes also has lastRegenTime which stores that last time player has requested to regenerate the health for their character.
  • AttackType stores the data related to each attack. It includes attack name, attack damage, and attack image displayed in the game.
  • SpecialAttackType is similar to AttackType but has one extra attribute i.e. - price. Since players have to buy special attacks from the marketplace, each special attack has a price marked.
  • allAttacks and allSpecialAttacks keeps the track of all the attacks and special attacks in the game. Keeping these in a map helps in reducing contract size as we will not store all the data associated with an attack multiple times for each character but we will store only the attack index which in effect reduces the contract transaction costs.
  • BigBoss struct contains all the data for the boss character.
  • defaultCharacters array contains the array of all the mintable characters that the player can choose from.
  • nftHolders is a map that holds the token ID for each address/player.
  • nftHolderAttributes holds the CharacterAttributes struct for each token ID minted by the players.
event CharacterNFTMinted( address sender, uint256 tokenId, uint256 characterIndex ); event AttackComplete(uint256 newBossHp, uint256 newPlayerHp); event RegenCompleted(uint256 newHp);
CharacterNFTMinted is an event that is emitted when a new character is minted by the player. AttackComplete is emitted when a player performs a normal attack or a special attack and RegenCompleted is emitted when a user has successfully called the claimHealth method.
constructor( string[] memory characterName, string[] memory characterImageURI, uint256[] memory characterMaxHp, uint256[][] memory characterAttacks, string memory bossName, string memory bossImageURI, uint256 bossHp, uint256 bossAttackDamage, address epicTokenAddress ) ERC721("Heroes", "HERO") { epicToken = epicTokenAddress; for (uint256 i = 0; i < characterName.length; i++) { CharacterAttributes memory charAttribute; charAttribute.characterIndex = i; = characterName[i]; charAttribute.imageURI = characterImageURI[i]; charAttribute.hp = characterMaxHp[i]; charAttribute.maxHp = characterMaxHp[i]; charAttribute.attacks = characterAttacks[i]; defaultCharacters.push(charAttribute); } _tokenIds.increment(); bigBoss = BigBoss({ name: bossName, imageURI: bossImageURI, hp: bossHp, maxHp: bossHp, attackDamage: bossAttackDamage }); }
  • In the constructor we are accepting arrays of characterName, characterImageURI, characterMaxHp and characterAttacks.
  • We will loop over these arrays and create CharacterAttributes instances and add them to the defaultCharacters array.
  • Note that the size/length of all these arrays should be the same.
  • We also accepts boss attributes like bossName, bossImageURI, bossHp, bossAttackDamage and create an instance of BigBoss struct.
  • We increment the _tokenIds so that it starts from 1.
  • At last, we need to accept the EPIC token address so that we can accept that token when the user mints the NFT or made any purchase from the marketplace.
  • Since we are accepting the EPIC token address in the NFTEpicGame contract, we have to deploy the token first and then use that address to deploy NFTEpicGame.
function addAttacks( // All the attacks for each character string[] memory attackNames, string[] memory attackImages, uint256[] memory attackDamages, uint256[] memory attackIndexes ) public onlyOwner { for (uint256 j = 0; j < attackIndexes.length; j++) { allAttacks.push( AttackType( attackIndexes[j], attackNames[j], attackDamages[j], attackImages[j] ) ); } } function addSpecialAttacks( // All the special attacks for each character string[] memory specialAttackNames, string[] memory specialAttackImages, uint256[] memory specialAttackDamages, uint256[] memory specialAttackPrices, uint256[] memory specialAttackIndexes ) public onlyOwner { for (uint256 j = 0; j < specialAttackIndexes.length; j++) { allSpecialAttacks.push( SpecialAttackType( specialAttackPrices[j], specialAttackIndexes[j], specialAttackNames[j], specialAttackDamages[j], specialAttackImages[j] ) ); } }
  • Both addAttacks and addSpecialAttacks are used to add attacks and special attacks to the game.
  • Note that both these methods have an onlyOwner modifier, which means only the deploying address can call these methods and add new attacks and special attacks.
  • Both these methods accept arrays of data like name, image, damage, indexes, and loop over them to create respective struct instances and add them to the allAttacks array or the allSpecialAttacks array.
function mintCharacterNFT(uint256 _characterIndex) external payable { require( _characterIndex < defaultCharacters.length, "Character index out of bounds" ); require( IERC20(epicToken).allowance(msg.sender, address(this)) >= 10 ether, "Please approve the required token transfer before minting" ); IERC20(epicToken).transferFrom(msg.sender, address(this), 10 ether); uint256 newItemId = _tokenIds.current(); _safeMint(msg.sender, newItemId); nftHolderAttributes[newItemId] = CharacterAttributes({ characterIndex: _characterIndex, name: defaultCharacters[_characterIndex].name, imageURI: defaultCharacters[_characterIndex].imageURI, hp: defaultCharacters[_characterIndex].hp, maxHp: defaultCharacters[_characterIndex].maxHp, attacks: defaultCharacters[_characterIndex].attacks, specialAttacks: defaultCharacters[_characterIndex].specialAttacks, lastRegenTime: block.timestamp }); nftHolders[msg.sender] = newItemId; _tokenIds.increment(); emit CharacterNFTMinted(msg.sender, newItemId, _characterIndex); }
mintCharacterNFT is called by all the players once they join the game. In mintCharacterNFT we have defined that to mint a new character user has to pay 10 EPIC tokens. This is what happens in the mintCharacterNFT method -
  • mintCharacterNFT accepts the character index that the player wants to mint and makes sure that the index is not out of bounds.
  • Next, it checks the allowance of epicToken is greater than or equal to 10 EPIC tokens, if not methods revert with an error message.
  • If the contract has allowance then we call the transferFrom method of ERC20 token and transfer 10 EPIC tokens from the player's account to the contract address.
  • Once all the checks are completed, we get the current token ID and call the _safeMint method of the ERC721 contract with msg.sender and token Id. This call will essentially mint a new NFT for the player.
  • After minting a new NFT character we have to create a new CharacterAttributes instance and use the defaultCharacters to fetch the metadata of that player.
  • Now that we have a new instance of CharacterAttributes we have to add it to nftHolderAttributes corresponding to the current token ID.
  • Finally, we can map the player's address to the token ID in the nftHolders map and increment the _tokenIds.
function claimHealth() external { require( nftHolders[msg.sender] != 0, "You don't have a character to claim health" ); require( IERC20(epicToken).allowance(msg.sender, address(this)) >= 0.1 ether, "Please approve the required token transfer before minting" ); IERC20(epicToken).transferFrom(msg.sender, address(this), 0.1 ether); uint256 tokenId = nftHolders[msg.sender]; CharacterAttributes memory character = nftHolderAttributes[tokenId]; uint256 currentTime = block.timestamp; uint256 timeSinceLastRegen = currentTime - character.lastRegenTime; if (timeSinceLastRegen > regenTime) { uint256 newHp = character.hp + timeSinceLastRegen.div(60); if (newHp > character.maxHp) { newHp = character.maxHp; } character.hp = newHp; character.lastRegenTime = currentTime; nftHolderAttributes[tokenId] = character; emit RegenCompleted(newHp); } }
claimHealth can be called by any character holder to gain some health for their player. claimHealth provides 1 HP for each minute since the player has called the claimHealth method. This means if the user has last called the claimHealth method after 20 minutes, then the player's character will have 20 new HP points. Note that the addition of these new HP points cannot go more than the maxHp of that character.
Each time a player wants to call the claimHealth method they have to pay a fee of 0.1 EPIC tokens.
  • In claimHealth first, we make sure that the calling player has a character minted and the player has approved the 0.1 EPIC token for the contract.
  • We have to call the transferFrom method of the ERC20 token to transfer 0.1 EPIC tokens from the player's wallet to the contract address. Once the tokens are transferred we have to retrieve the tokenId of the player from the nftHolders map.
  • Using tokenId we can fetch the character struct from nftHolderAttributes map. character has lastRegenTime which can be used to calculate the time elapsed since the player has called the claimHealth method.
  • If it's been more than regenTime which is 60 seconds in our case, we allow them to claim the health.
  • To calculate the new HP for the character we have to divide timeSinceLastRegen by 60 since timeSinceLastRegen is the seconds elapsed since the player has claimed the health and add that number to the current HP of the player.
  • If the newHp is more than the maxHp of that player we give maxHp to that character. At the end we have to update the lastRegenTime to currentTime and update nftHolderAttributes with current character.
function attackBoss(uint256 attackIndex) public { uint256 nftTokenIdOfPlayer = nftHolders[msg.sender]; CharacterAttributes storage player = nftHolderAttributes[ nftTokenIdOfPlayer ]; require(player.hp > 0, "Error: character must have HP to attack boss."); require(bigBoss.hp > 0, "Error: boss is already dead"); uint256 attackDamage = 0; for (uint256 i = 0; i < player.attacks.length; i++) { if (attackIndex == player.attacks[i]) { attackDamage = allAttacks[attackIndex].attackDamage; } } require(attackDamage > 0, "Error: attack must have damage."); if (bigBoss.hp < attackDamage) { bigBoss.hp = 0; } else { bigBoss.hp = bigBoss.hp - attackDamage; } if (player.hp < bigBoss.attackDamage) { player.hp = 0; } else { player.hp = player.hp - bigBoss.attackDamage; } emit AttackComplete(bigBoss.hp, player.hp); }
attackBoss is called when a player uses any normal attack on the boss. Any player can only attack the boss if the player and boss both have more than 0 HP points.
  • First, we retrieve the current character instance of nftHolderAttributes and check all the requirements.
  • attackBoss accepts the attackIndex which corresponds to the attack player wants to perform on the boss.
  • To get the attackDamage from attackIndex we have to loop over all the available attacks of that character and make sure that the player has called the method with the correct attackIndex.
  • Once we have attackDamage we have to make sure that attackDamage is more than 0 or else revert the method call.
  • The only condition attackDamage can be 0 is when attackIndex is not present in allAttacks.
  • In the end, reduce attackDamage from the boss's HP and reduce the boss's attack damage from the character's HP.
attackSpecialBoss is similar to attackBoss. Only difference is instead of fetching attackDamage from allAttacks, we fetch it from allSpecialAttacks
function buySpecialAttack(uint256 specialAttackIndex) public payable { uint256 nftTokenIdOfPlayer = nftHolders[msg.sender]; require( nftTokenIdOfPlayer > 0, "Error: must have NFT to buy special attack." ); CharacterAttributes storage player = nftHolderAttributes[ nftTokenIdOfPlayer ]; require( IERC20(epicToken).allowance(msg.sender, address(this)) >= allSpecialAttacks[specialAttackIndex].price, "Error: user must provide enough token to buy special attack." ); IERC20(epicToken).transferFrom( msg.sender, address(this), allSpecialAttacks[specialAttackIndex].price ); player.specialAttacks.push(specialAttackIndex); emit AttackComplete(bigBoss.hp, player.hp); }
buySpecialAttack is the method called from the marketplace, where the player can buy and special attack for their character. Each special attack has a price associated with it in EPIC tokens and the player has to approve that price to purchase the special attack.
Once we confirm that the user has approved the special attack's price we make a transferFrom call to transfer the token and push the special attack index in the specialAttacks array of the player's character.
function checkIfUserHasNFT() public view returns (CharacterAttributes memory) { uint256 userNftTokenId = nftHolders[msg.sender]; if (userNftTokenId > 0) { return nftHolderAttributes[userNftTokenId]; } else { CharacterAttributes memory emptyStruct; return emptyStruct; } } function getAllDefaultCharacters() public view returns (CharacterAttributes[] memory) { return defaultCharacters; } function getAllAttacks() public view returns (AttackType[] memory) { return allAttacks; } function getAllSpecialAttacks() public view returns (SpecialAttackType[] memory) { return allSpecialAttacks; } function getBigBoss() public view returns (BigBoss memory) { return bigBoss; }
These all are the helper functions to read the data from the contract:
checkIfUserHasNFT checks if the player has minted NFT before, if yes then it returns the CharacterAttributes instance of the minted NFT or else returns an empty instance of CharacterAttributes. getAllDefaultCharacters method returns an array of all the available characters that the user can mint. getAllAttacks and getAllSpecialAttacks returns arrays of allAttacks and allSpecialAttacks respectively. getBigBoss simply returns the bigBoss variable.
function tokenURI(uint256 _tokenId) public view override returns (string memory) { CharacterAttributes memory charAttributes = nftHolderAttributes[ _tokenId ]; string memory strHp = Strings.toString(charAttributes.hp); string memory strMaxHp = Strings.toString(charAttributes.maxHp); string memory specialAttacksStr = ""; string memory attacksStr = ""; for (uint256 i = 0; i < charAttributes.specialAttacks.length; i++) { uint256 index = charAttributes.specialAttacks[i]; specialAttacksStr = string( abi.encodePacked( specialAttacksStr, ', {"trait_type": "Special Attack - ', allSpecialAttacks[index].specialAttackName, '", "value": ', Strings.toString( allSpecialAttacks[index].specialAttackDamage ), "}" ) ); } for (uint256 i = 0; i < charAttributes.attacks.length; i++) { uint256 index = charAttributes.attacks[i]; attacksStr = string( abi.encodePacked( attacksStr, ', {"trait_type": "', allAttacks[index].attackName, '", "value": ', Strings.toString(allAttacks[index].attackDamage), "}" ) ); } string memory json = Base64.encode( bytes( string( abi.encodePacked( '{"name": "',, " -- NFT #: ", Strings.toString(_tokenId), '", "description": "This is an NFT that lets people play in the Epic NFT Game!", "image": "', charAttributes.imageURI, '", "attributes": [{"trait_type": "Health Points", "value": ', strHp, ', "max_value": ', strMaxHp, "}", specialAttacksStr, attacksStr, "]}" ) ) ) ); string memory output = string( abi.encodePacked("data:application/json;base64,", json) ); return output; }
The tokenURI on an NFT is a unique identifier of what the token "looks" like. A URI could be an API call over HTTPS, an IPFS hash, or anything else unique. tokenURI will return something like this -
{ "name": "Spider Man -- NFT #: 1", "description": "This is an NFT that lets people play in the Epic NFT Game!", "image": "", "attributes": [ { "trait_type": "Health Points", "value": 300, "max_value": 300 }, { "trait_type": "Special Attack - Bomb Attack", "value": 80 }, { "trait_type": "Special Attack - Explosion Attack", "value": 100 }, { "trait_type": "Punch", "value": 50 }, { "trait_type": "Spider Attack", "value": 55 }, { "trait_type": "Web Shooter", "value": 65 } ] }
The JSON show what an NFT looks like and its attributes. The image section points to a URI of what the NFT looks like. In our case, we will be using Arweave to store all the images and use the URI provided by Arweave. This makes it easy for NFT marketplace platforms like Opensea, Rarible, and Mintable to render NFTs on their platform and show all the attributes of those NFTs since they are all looking for this metadata.
In this function, we do string manipulation magic to create a JSON string and then convert it to Base64 and attach data:application/json;base64, at the from so that our browser knows how to handle the base64 string. Note that this format is recommended by big NFT marketplaces to render the NFT with all the metadata.
In the end, we will quickly deploy this contract on Rinkby Testnet, mint a new character, and check the NFT on the Opensea marketplace.
This is all we need to do in NFTEpicGame.sol. Now let's write a script for hardhat to deploy this contract in a local blockchain to develop the frontend app.

Compiling and deploying with Hardhat

Open scripts/run.ts, delete all the contracts and paste the following code -
In run.ts we will deploy out both contracts on local blockchain for development.
const epicTokenFactory = await ethers.getContractFactory("EPICToken"); const epicToken = await epicTokenFactory.deploy("EPIC Token", "EPIC"); const gameContractFactory = await ethers.getContractFactory("NFTEpicGame");
First, we get the Contract Factory for EPICToken and then call the deploy method and pass-in token name and token symbol in the constructor. Once the EPIC token is deployed we can start the deployment process of NFTEpicGame since NFTEpicGame requires EPICToken contract address.
In the const gameContract = await gameContractFactory.deploy() call we are passing all the required data we need in the constructor of the NFTEpicGame contract. If you notice for characterImageURI we are using URLs. In the next section, we will cover how to upload images in arweave and get the image URLs.
Once NFTEpicGame is deployed we need to make two contract calls before anyone can use this contract. We need to add attacks and special attacks. You might think we should have accepted this data in the contract constructor, but solidity only accepts up to 15 arguments in the contract constructor, hence we have created two separate methods to add attacks and special attacks. Doing so gives us the flexibility of updating special attacks in the marketplace anytime we want.
That's all we are doing in run.ts, deploying two smart contracts and calling addAttacks and addSpecialAttacks which sets up the game characters.

Uploading images to Arweave

All the assets used in this game can be found here.
We will use ArDrive to upload images manually on the Arweave network and use the URLs provided ArDrive in our contracts. To use ArDrive, you will need an Arweave account and Arweave keys json file. If you don't have an Arweave account, go to and create an account. You will have to upload the keys in ArDrive to log in and start uploading images.
When you use Arweave Faucet to create an account you also get 0.2 AR tokens which are more than enough to upload more than 2000 Images on ArDrive.
Login to ArDrive, if you are a new user it will ask for username and password. Once you have access to the dashboard you can upload the image in the dashboard and click on the preview button to get the image URL. Use these URLs in the run.ts for characters and attacks.

Running contracts locally

To run the contracts locally run the following command.
npx hardhat node
This will start a local blockchain and print out 20 testing account addresses and their private keys.
Copy one of these private keys, go to Metamask and click on the Import Account button and paste the private key. Make sure you are connected to the localhost:8454 blockchain in Metamask.
Note: chain id of hardhat blockchain is 31337 and default chain id for localhost:8454 in Metamask is 1337. To change the chain id, go to Setting > Networks > Localhost 8454. There you can change 1337 to 31337.
To deploy the contacts on the hardhat local blockchain, we need to run the run.ts.
npx hardhat run scripts/run.ts --network localhost
This will deploy both contracts and print the contract address in the terminal. Note these addresses.

Building Frontend

In our game, we will have four pages.
/ - pages/index.tsx is the home page that shows features and some information about the game. Nothing much is happening here. /faucet - pages/faucet.tsx is the faucet page where players can mint new tokens. /market-place - pages/market-place.tsx is the place where players can buy new special attacks for their characters. /play - pages/play.tsx is the game arena where if the user has character minted they can fight with the boss or else they can mint a new character.
In this tutorial, we will try to separate business logic with our frontend UI code. We will create a global context that will have all the necessary data fetched from the NFTEpicGame contract as well as all the method calls.

Business Logic

Create a file contexts/DappContext.tsx and paste the following code -
Typescript might be yelling for some imports errors, but bear with me, we will solve all the errors. Let's break the DappContext and see what's happening -
const checkIfWalletIsConnected = useCallback(async () => { try { const { ethereum } = window; if (!ethereum) { console.log("Make sure you have MetaMask!"); setIsLoading(false); return; } else { console.log("We have the ethereum object", ethereum); const accounts = await ethereum.request({ method: "eth_requestAccounts", }); if (accounts.length !== 0) { const account = accounts[0]; console.log("Found an authorized account:", account); setCurrentAccount(account); } else { console.log("No authorized account found"); } } checkNetwork(); } catch (err) { console.log(err); } }, []);
checkIfWalletIsConnectedcheck if the metamask is installed in the user's browser and if it does then get the account and set the currentAccount state variable.
const connectWalletAction = async () => { try { const { ethereum } = window; if (!ethereum) { alert("Get MetaMask!"); return; } const accounts = await ethereum.request({ method: "eth_requestAccounts", }); console.log("Connected", accounts[0]); setCurrentAccount(accounts[0]); } catch (err) { console.log(`err`, err); } };
connectWalletAction is used when the user has rejected to connect the wallet when the website opens and then chooses to connect the wallet from the Connect Wallet button.
const fetchBalance = async () => { var balance: string; if (tokenContract) { balance = await tokenContract.balanceOf(currentAccount); } else { const provider = new ethers.providers.Web3Provider(window.ethereum); const signer = provider.getSigner(); const contract = new ethers.Contract( TOKEN_CONTRACT_ADDRESS, epicToken.abi, signer ); balance = await contract.balanceOf(currentAccount); setTokenContract(contract); } console.log("Balance is : ", balance.toString()); setCurrentBalance(balance.toString()); };
fetchBalance is used to fetch the EPIC token balance of the user. In the function, we will check if the token contract is present in the state variable or not. If we found a token contract instance then we will use it and make a balanceOf call to fetch the user's balance or else we will create a new instance of token contract, set the state variable and then fetch the token balance. Once we have the token balance we can set the currentBalance state variable.
const fetchData = async () => { var data = await gameContract.checkIfUserHasNFT(); var character = parseDefaultCharacter(data); if ( == "") { setHasCharacter(false); var allDefaultCharacters = await gameContract.getAllDefaultCharacters(); var characterList: CharacterProps[] = []; allDefaultCharacters.forEach((element) => { characterList.push(parseDefaultCharacter(element)); }); setDefaultCharactersList(characterList); } else { setHasCharacter(true); setCurrentCharacter(parseDefaultCharacter(data)); } var bossData = await gameContract.getBigBoss(); var boss = parseBigBoss(bossData); setBigBoss(boss); // Fetch all the attacks and special attacks var data = await gameContract.getAllAttacks(); var attacks = []; data.forEach((element) => { attacks.push(parseAttacks(element)); }); setAllAttacks(attacks); var data = await gameContract.getAllSpecialAttacks(); var specialAttacks = []; data.forEach((element) => { specialAttacks.push(parseSpecialAttacks(element)); }); setAllSpecialAttacks(specialAttacks); setIsLoading(false); };
fetchData is used to fetch all the necessary data from the NFTEpicGame contract. This is what's happening here -
  • Make a contract call to checkIfUserHasNFT to check if the user has minted character NFT or not.
  • If checkIfUserHasNFT returns empty struct then we fetch the default characters by making method call to getAllDefaultCharacters.
  • If we get a valid struct from checkIfUserHasNFT then we send the returned data to parseDefaultCharacter which takes the raw data and returns the object with the CharacterProps type. We are doing this just to make typescript happy.
  • Next, fetch the attributes of the boss by making a method call to getBigBoss.
  • At the end we fetch all the attacks and special attacks via respective contract method calls, parse the objects, and set the state variables.
  • Don't worry, we will write all the parse functions shortly.
const faucet = async () => { if (BigNumber.from(currentBalance).gte(ethers.utils.parseEther("20"))) { toast( `You already have ${ethers.utils.formatEther( BigNumber.from(currentBalance) )} tokens. Please use that first.`, { draggable: true, closeOnClick: true, autoClose: 3500, progress: undefined, type: "error", } ); } else { const id = toast.loading("Please wait..."); var txn = await tokenContract.faucet( currentAccount, ethers.utils.parseEther("20") ); await txn.wait(); await fetchBalance(); toast.update(id, { render: "20 EPIC token added to your wallet", type: "success", isLoading: false, draggable: true, closeOnClick: true, autoClose: 3500, }); } };
faucet method is used to call the faucet method of EPIC token. Before making a call, we have to make sure that the user has less than 20 EPIC tokens in their wallet, or else the method call to the contract will revert with an error.
Here we will show a toast notification until new tokens are minted and once tokens are minted we make a call to fetchBalance, which will fetch the balance again and update the state variable.
const mintCharacterNFT = async (characterIndex: BigNumber) => { if (BigNumber.from(currentBalance) < ethers.utils.parseEther("10")) { toast( `You don't have enough tokens to mint a character. Please get more tokens.`, { draggable: true, closeOnClick: true, autoClose: 3500, progress: undefined, type: "error", } ); } else { var txn = await tokenContract.approve( gameContract.address, ethers.utils.parseEther("10") ); await txn.wait(); txn = await gameContract.mintCharacterNFT(characterIndex.toNumber()); await txn.wait(); setIsLoading(true); toast(`AVENGERS....`, { draggable: true, closeOnClick: true, autoClose: 3000, progress: undefined, type: "success", }); setTimeout(async () => { toast(`ASSEMBLE....`, { draggable: true, closeOnClick: true, autoClose: 3000, progress: undefined, type: "success", }); }, 3000); setTimeout(async () => { await fetchData(); setIsLoading(false); }, 6000); } };
  • mintCharacterNFT is used to mint new character NFT for users on the /play page.
  • Each time a user mints an NFT they have to pay 10 EPIC tokens, hence we verify that the user has more than 10 EPIC tokens present in their wallet.
  • Since the EPIC token is an ERC20 token, we will have to call approve a method for 10 EPIC tokens, so that our contract can call the transferFrom method and accept these tokens. If you are confused about how this works, refer to this video.
  • After approving the tokens, we have to make and call to mintCharacterNFT method from the NftEpicGame contract and pass in the characterIndex from defaultCharactersList.
  • After the method call, we have minted a new NFT for that user, so we need to make a call to fetchData which will fetch all the data again, and set the necessary state variable which allows us to change the UI dynamically for better user experience.
const attackBoss = async (attackIndex: BigNumber) => { var txn = await gameContract.attackBoss(attackIndex.toNumber()); txn.wait().then(async () => { await fetchData(); }); }; const attackBossWithSpecialAttack = async (attackSpecialIndex: BigNumber) => { var txn = await gameContract.attackSpecialBoss( attackSpecialIndex.toNumber() ); txn.wait().then(async () => { await fetchData(); }); };
attackBoss and attackBossWithSpecialAttack both accepts the attack index and call the attackBoss or attackSpecialBoss respectively to perform attack action. Note that we are making a call to fetchData because we need to update the HP point of both player's character and boss.
const claimHealth = async () => { const id = toast.loading("Please wait..."); var txn = await tokenContract.approve( gameContract.address, ethers.utils.parseEther("0.1") ); await txn.wait(); txn = await gameContract.claimHealth(); await txn.wait(); toast.update(id, { render: "Successfully Recovered Health", type: "success", isLoading: false, draggable: true, closeOnClick: true, autoClose: 3000, }); fetchData(); };
The claimHealth method does two things, make an approve call for 0.1 EPIC token and then call the claimHealth method call from the NFTEpicGame contract. In the end, we need to call fetchData again since the HP of the user is updated and we have to update the UI.
const fetchSpecialAttacks = async () => { const data = await gameContract.getAllSpecialAttacks(); const specialAttacks: SpecialAttackProps[] = []; data.forEach((element) => { specialAttacks.push(parseSpecialAttacks(element)); }); return specialAttacks; }; const buySpecialAttack = async (price: BigNumber, index: BigNumber) => { if (BigNumber.from(currentBalance).lt(price)) { toast( `You don't have enough tokens to mint a character. Please get more tokens.`, { draggable: true, closeOnClick: true, autoClose: 3500, progress: undefined, type: "error", } ); } else { const id = toast.loading("Please wait..."); var txn = await tokenContract.approve(gameContract.address, price); await txn.wait(); txn = await gameContract.buySpecialAttack(index); await txn.wait(); toast.update(id, { render: "Successfully bought special attack", type: "success", isLoading: false, draggable: true, closeOnClick: true, autoClose: 3000, }); } };
fetchSpecialAttacks and buySpecialAttack are used on the marketplace screen.
  • fetchSpecialAttacks makes a call to the getAllSpecialAttacks method and returns the parsed data.
  • buySpecialAttack accepts the price and index of the special attack user wishes to buy and checks if the user has enough EPIC tokens to make the purchase.
  • If the user has enough balance, we have to make an approve call for the attack's price and then call buySpecialAttack with the index value to add the special attack for that player's character.
useEffect(() => { setIsLoading(true); checkIfWalletIsConnected(); }, [checkIfWalletIsConnected]); useEffect(() => { const getGameContract = async () => { const provider = new ethers.providers.Web3Provider(window.ethereum); const signer = provider.getSigner(); const contract = new ethers.Contract( GAME_CONTRACT_ADDRESS, nftEpicGame.abi, signer ); setGameContract(contract); }; if (currentAccount) { getGameContract(); fetchBalance(); } }, [currentAccount, hasCharacter]);
useEffect is called when the webpage is loaded or when a specific variable changes its value. Here in the first useEffect will run when the page is loaded and calls checkIfWalletIsConnected. checkIfWalletIsConnected will fetch the user account from metamask and set the state variable. The second useEffect will only run when we have the currentAccount variable set. In this, we get create an instance of the game contract and fetch the EPIC token balance.
useEffect(() => { if (gameContract) { fetchData(); } }, [gameContract, hasCharacter]);
Lastly, this useEffect will only run when we have gameContract or when hasCharacter value changes. We need to check hasCharacter because when the user has minted a new character then hasCharacter changes and we need to fetch all the new data.
That's all the business logic we need. Let's look at some helper functions and types needed in our context.
// /utils/helper.ts import { BigNumber } from "ethers"; import attackAnimationOne from "../utils/attack-animation-1.json"; import attackAnimationTwo from "../utils/attack-animation-2.json"; import attackAnimationThree from "../utils/attack-animation-3.json"; import { AttackProps, BigBoss, CharacterProps, SpecialAttackProps, } from "./contracts"; export const parseDefaultCharacter = (data: any): CharacterProps => { var res: CharacterProps = { attacks: data.attacks, characterIndex: data.characterIndex, hp: data.hp, imageURI: data.imageURI, maxHp: data.maxHp, name:, specialAttacks: data.specialAttacks, lastRegenTime: data.lastRegenTime, }; return res; }; export const parseAttacks = (data: any): AttackProps => { var res: AttackProps = { attackDamage: data.attackDamage, attackIndex: data.attackIndex, attackImage: data.attackImage, attackName: data.attackName, }; return res; }; export const parseSpecialAttacks = (data: any): SpecialAttackProps => { var res: SpecialAttackProps = { price: data.price, specialAttackDamage: data.specialAttackDamage, specialAttackIndex: data.specialAttackIndex, specialAttackImage: data.specialAttackImage, specialAttackName: data.specialAttackName, }; return res; }; export const parseBigBoss = (data: any): BigBoss => { var res: BigBoss = { attackDamage: data.attackDamage, imageURI: data.imageURI, hp: data.hp, maxHp: data.maxHp, name:, }; return res; }; export const getAttackAnimation = (attackIndex: BigNumber) => { if (attackIndex.toNumber() == 0) { return attackAnimationOne; } else if (attackIndex.toNumber() == 1) { return attackAnimationTwo; } else if (attackIndex.toNumber() == 2) { return attackAnimationThree; } else if (attackIndex.toNumber() == 3) { return attackAnimationOne; } else if (attackIndex.toNumber() == 4) { return attackAnimationTwo; } else if (attackIndex.toNumber() == 5) { return attackAnimationThree; } else if (attackIndex.toNumber() == 6) { return attackAnimationOne; } else if (attackIndex.toNumber() == 7) { return attackAnimationTwo; } else if (attackIndex.toNumber() == 8) { return attackAnimationThree; } };
Here parseDefaultCharacter, parseAttacks, parseSpecialAttacks, and parseBigBoss are used to convert the raw data from contract call into typed objects for typescript. getAttackAnimation is used to get the Lottie animation file that we show when the user performs any action.
// /utils/contracts.ts import { BigNumber, ethers } from "ethers"; export interface DappContextProps { currentAccount: string | null; isLoading: boolean; currentBalance: string; currentCharacter: CharacterProps; defaultCharactersList: CharacterProps[]; hasCharacter: boolean; gameContract: ethers.Contract | null; allAttacks: AttackProps[]; allSpecialAttacks: SpecialAttackProps[]; bigBoss: BigBoss; connectWalletAction: () => Promise<void>; faucet: () => Promise<void>; mintCharacterNFT: (characterIndex: BigNumber) => Promise<void>; attackBoss: (attackIndex: BigNumber) => Promise<void>; attackBossWithSpecialAttack: (attackSpecialIndex: BigNumber) => Promise<void>; claimHealth: () => Promise<void>; fetchSpecialAttacks: () => Promise<SpecialAttackProps[]>; buySpecialAttack: (price: BigNumber, index: BigNumber) => Promise<void>; } export interface AttackProps { attackIndex: BigNumber; attackName: string; attackDamage: BigNumber; attackImage: string; } export interface SpecialAttackProps { price: BigNumber; specialAttackIndex: BigNumber; specialAttackName: string; specialAttackDamage: BigNumber; specialAttackImage: string; } export interface CharacterProps { characterIndex: BigNumber; name: string; imageURI: string; hp: BigNumber; maxHp: BigNumber; attacks: BigNumber[]; specialAttacks: BigNumber[]; lastRegenTime: BigNumber; } export interface BigBoss { name: string; imageURI: string; hp: BigNumber; maxHp: BigNumber; attackDamage: BigNumber; }
This file contains all the interfaces we will need in our code.
// /utils/constants.ts // Add your smart contract address here export const GAME_CONTRACT_ADDRESS = "0x6901351923a0cd5312776498CE750fe821De4fC0"; export const TOKEN_CONTRACT_ADDRESS = "0x870AF25D3AD800a19b03e071467b94E8a9717383";
This is where we store our contract addresses. When we deploy to either local blockchain or mainnet/testnet, we have to update the contract address in this file.

Fontend Logic

Before we start, we will have t use the DappContext that we have created on our game. Open _app.tsx and paste the following code.
import type { AppProps } from "next/app"; import { useRouter } from "next/router"; import { ToastContainer } from "react-toastify"; import "react-toastify/dist/ReactToastify.css"; import { DappProvider } from "../contexts/DappContext"; import "../styles/globals.css"; function MyApp({ Component, pageProps }: AppProps) { var { route } = useRouter(); if (route != "/") { return ( <DappProvider> <ToastContainer position="top-right" autoClose={5000} hideProgressBar={false} newestOnTop={false} closeOnClick rtl={false} pauseOnFocusLoss draggable pauseOnHover limit={1} /> {/* Same as */} <ToastContainer /> <Component {...pageProps} /> </DappProvider> ); } else return <Component {...pageProps} />; } export default MyApp;
In _app.tsx we are wrapping our Component with DappProvider as we need all the variables and functions from our DappContext. Notice that we are only wrapping with DappProvider if the current route is not /, i.e current page is not the home page. As we are not doing anything except showing some images and data about the website on the home page we don't need any data from the context there.
NFT Game Home Page
Nothing cool happening here, just loading some UI components.
Here, we are making a common UI for the navbar and a container to show the current account address connected with the website.
NFT Game Faucet Page
The faucet page is used to get some EPIC tokens. On this page, we show the user their EPIC token balance and a button to request more. Users can only request new EPIC tokens if they have less than 20 tokens. With the click of the Mint button, we are calling the faucet function from DappContext.
NFT Game Marketplace Page
On the marketplace, we are just fetching all the special attack lists, rendering the UI for each attack, and making a buySpecialAttack call from the useDapp hook to approve and buy the special attack. Nothing fancy here.
// pages/play.tsx import Head from "next/head"; import React from "react"; import "react-step-progress-bar/styles.css"; import GameArena from "../components/GameArena"; import { Loader } from "../components/Loader"; import MintCharacter from "../components/MintCharacter"; import { useDapp } from "../contexts/DappContext"; function Play() { const { currentAccount, hasCharacter, connectWalletAction, isLoading } = useDapp(); if (isLoading) { return <Loader />; } return ( <> <Head> <title>Epic NFT Game</title> <meta name="description" content="Epic NFT Game" /> <link rel="icon" href="/favicon.ico" /> </Head> {!currentAccount ? ( <div className="h-screen bg-gray-800 text-center overflow-auto"> <div className="mx-auto max-w-7xl"> <div className="h-screen flex justify-center items-center"> <button className="font-game text-6xl text-pink-600 hover:text-yellow-600" onClick={() => { connectWalletAction(); }} > Connect wallet to play </button> </div> </div> </div> ) : hasCharacter ? ( <GameArena /> ) : ( <MintCharacter /> )} </> ); } export default Play;
play.ts is the game arena where players can mint a new character and fight against the boss. On this page, if the user has minted a character then we will show them GameArena or else we will show them the MintCharacter component.
NFT Game Mint Character
On this page, we have two components, MintCharacter and CharacterItem. MintCharacter just has the UI for the background and faucet button. We are fetching the defaultCharactersList, looping over it, and rendering the CharacterItem component.
CharacterItem returns the image of that character and the name. In this component, we are also adding a confirmation modal for each character, which will show the price of that character and allow the user to call the mint method of the smart contract.
In MintConfirmationModal we show a button to mint the character and on click of that button, we call the mintCharacterNFT method from out DappContext.
NFT Game Arena
GameArena is the main page where all the magic happens. We have four components here - GameArena, AttackAnimation, AttackItem and SpecialAttackItem.
  • GameArena renders the background, health bar, title, and claim health button.
  • AttackAnimation is the animation that is shown when an attack is in progress.
  • AttackItem and SpecialAttackItem are just attack buttons that users can click on and make respective contract calls to act.
Let's break this down. When a player performs an attack action, we have to do two things, make a method call to contract and show the animation on top of characters. We have developed our attack method in such a way that when a player attacks the boss, the boss will attack the character in the same transaction to remove that extra transaction and save on transaction fees. This means we first have to show an attack animation on the boss and then show it on the player as well.
To handle this animation display logic, we have three state variables, attackOnBoss, attackOnCharacter, and attackIndex.
  • attackOnBoss and attackOnCharacter are boolean variables then will be set when we want to show the animation. By default both of these variables are false.
  • When we make an api call, we make the attackOnBoss true, and in our UI, we have made a check that if attackOnBoss is true we will render the Lottie animation.
  • Each attack can have a different animation. We will be using the getAttackAnimation method from our helper.ts file to get the relevant animation for that attack.
  • Once the contract call is completed we can set the attackOnBoss to false and set attackOnCharacter to true for a few seconds. This will essentially remove the Lottie animation from the boss and show it on the character.
  • We are also maintaining the attackIndex which will be used to get the relevant Lottie animation for the attack.
When an attack is in progress we give a little shake effect on the boss, and for that, we are using react-spring. You can learn more about react-spring and small animations here.
HealthBar simply shows a progress bar for the HP point of character and boss. We are using react-step-progress-bar for rendering the bar.
NFT Game Claim Health
ClaimHealthModal is a modal, that shows the HP that can be claimed by the player. To calculate the claimable HP, we have to subtract the current timestamp with the lastRegenTime of that character and convert it to minutes. The minutes that have been passed since the user has claimed the health is the claimable HP. Once the user chooses to claim the health we can make a claimHealth call, which will approve 0.1 EPIC token and call the claimHealth method of our contract.
The last component that we have is the Loader component. Create a file called Loader.tsx in the components folder and add the following code.
// /components/Loader.tsx import React from "react"; import Lottie from "react-lottie"; import loaderAnimation from "../utils/loader.json"; export const Loader = () => { const defaultOptions = { loop: true, autoplay: true, animationData: loaderAnimation, rendererSettings: { preserveAspectRatio: "xMidYMid slice", }, }; return ( <> <div className="h-screen bg-gray-800 text-center"> <div className="w-full h-full flex justify-center items-center"> <Lottie options={defaultOptions} height={400} width={400} /> </div> </div> </> ); };
In Loader.tsx we are simply rendering a Lottie animation in the center of the page.
This sums up our UI code. Let's deploy our contract on ``Avalanche FUJI C-Chain.

Deploy contract on Avalanche

Create a file called deploy.ts in the scripts folder and paste the following code.
We already have a run.ts script with almost the same code but it's always a better idea to create a separate script for deployment and local development.
Next this is to add Avalanche FUJI C-Chain in the metamask. Follow this article if you are facing difficulty adding network in metamask.
Now we need to export our metamask account's private key. Create a new file called .env in the root folder and paste the private key as shown below.
Next, we need to configure hardhat.config.ts to point to Avalanche testnet. Open hardhat.config.ts and paste the following code.
import "@nomiclabs/hardhat-waffle"; import dotenv from "dotenv"; dotenv.config({ path: ".env" }); export default { solidity: { version: "0.8.0", settings: { optimizer: { enabled: true, runs: 200, }, }, }, networks: { hardhat: { allowUnlimitedContractSize: true, }, avaxFujiTestnet: { allowUnlimitedContractSize: true, url: "", accounts: [process.env.ACCOUNT_PRIVATE_KEY], }, rinkby: { allowUnlimitedContractSize: true, url: "", accounts: [process.env.ACCOUNT_PRIVATE_KEY], }, }, };
Here we have configured Avalanche and Ethereum testnet for deployment. If you wish to test your NFTs on Opensea, you can deploy our contract on the Rinkby network, mint a character and check the Opensea for the NFT details. Here is an example for you.
OpenSea Example
To deploy the contract on Avalanche testnet, run the following code in the terminal.
npx hardhat run scripts/deploy.ts --network avaxFujiTestnet
This command will print the contract address for both our contracts. Copy these addresses and update utils/constants.ts for the contract to work in the desired network.
Here comes the end of this long tutorial. Here is our game in action.
Video: The Epic Nft Game Demo
You can find the source code of the game here.


Congratulation on making it to the end of this very long tutorial and thank you for taking this journey with me. In this tutorial, we have learned how to create NFT based gaming contract. how to create an ERC20 token, how to create a beautiful UI for the game, and deploy our contract on Avalanche testnet.
Keep building on Web3. #WAGMI

About the Author

I'm Viral Sangani, a tech enthusiast working on blockchain projects & love the Web3 community. Feel free to connect with me on Github.
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