How to Set Access Control, a Token URI, Pause, and Transfer an ERC-721 Token Using Hardhat (Part 2)

In this tutorial, you'll learn how to create and manage an advanced ERC-721 token smart contract using Hardhat and OpenZeppelin. We'll cover deploying the contract, minting NFTs, pausing and unpausing the contract, and transferring tokens. You'll gain experience with Access Control (admin, minting, pausing roles), URI storage, and Pausable functionalities.

You can take a look at the complete code in the Hedera-Code-Snippets repository.

Prerequisites

⚠️ Complete tutorial part 1 as we continue from this example.
Basic understanding of smart contracts.
Basic understanding of Node.js and JavaScript.
Basic understanding of Hardhat EVM Development Tool and Ethers.
ECDSA account from the Hedera Portal.

Video Tutorial

You can watch the video tutorial (which uses Hardhat version 2) or follow the step-by-step tutorial below (which uses Hardhat version 3).

🚧 What's new: Hardhat 2 → 3

Key differences in Hardhat 3:

compile → build npx hardhat compile is now npx hardhat build. This is the big one. The v3 migration guide explicitly shows using the build task.
project init switch v2 commonly used npx hardhat or npx hardhat init to bootstrap. In v3 it’s npx hardhat --init.

keystore helper commands are new v3’s recommended flow includes a keystore plugin with commands like npx hardhat keystore set HEDERA_RPC_URL and npx hardhat keystore set HEDERA_PRIVATE_KEY. These weren’t standard in v2.
Foundry-compatiable Solidity tests In addition to offering Javascript/Typescript integration tests, Hardhat v3 also integrates Foundry-compatible Solidity tests that allows developers to write unit tests directly in Solidity

Enhanced Network Management v3 allows tasks to create and manage multiple network connections simultaneously which is a significant improvement over the single, fixed connection available in version 2. This provides greater flexibility for scripts and tests that interact with multiple networks.

📚 Learn more from the official Hardhat documentation.

Step 1: Create and Compile the Solidity Contract

Create a new Solidity file named MyTokenAdvanced.sol in your contracts directory, and paste this Solidity code:

contracts/MyTokenAdvanced.sol

// SPDX-License-Identifier: MIT
// Compatible with OpenZeppelin Contracts ^5.0.0
pragma solidity ^0.8.28;

import {AccessControl} from "@openzeppelin/contracts/access/AccessControl.sol";
import {ERC721} from "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import {ERC721Pausable} from "@openzeppelin/contracts/token/ERC721/extensions/ERC721Pausable.sol";
import {ERC721URIStorage} from "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";

contract MyTokenAdvanced is ERC721, ERC721URIStorage, ERC721Pausable, AccessControl {
    bytes32 public constant PAUSER_ROLE = keccak256("PAUSER_ROLE");
    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
    uint256 private _nextTokenId;

    constructor(address defaultAdmin, address pauser, address minter)
        ERC721("MyTokenAdvanced", "MTK")
    {
        _grantRole(DEFAULT_ADMIN_ROLE, defaultAdmin);
        _grantRole(PAUSER_ROLE, pauser);
        _grantRole(MINTER_ROLE, minter);
    }

    function pause() public onlyRole(PAUSER_ROLE) {
        _pause();
    }

    function unpause() public onlyRole(PAUSER_ROLE) {
        _unpause();
    }

    function safeMint(address to, string memory uri)
        public
        onlyRole(MINTER_ROLE)
        returns (uint256)
    {
        uint256 tokenId = _nextTokenId++;
        _safeMint(to, tokenId);
        _setTokenURI(tokenId, uri);
        return tokenId;
    }

    // The following functions are overrides required by Solidity.

    function _update(address to, uint256 tokenId, address auth)
        internal
        override(ERC721, ERC721Pausable)
        returns (address)
    {
        return super._update(to, tokenId, auth);
    }

    function tokenURI(uint256 tokenId)
        public
        view
        override(ERC721, ERC721URIStorage)
        returns (string memory)
    {
        return super.tokenURI(tokenId);
    }

    function supportsInterface(bytes4 interfaceId)
        public
        view
        override(ERC721, ERC721URIStorage, AccessControl)
        returns (bool)
    {
        return super.supportsInterface(interfaceId);
    }
}

The contract implements the ERC721URIStorage, ERC721Pausable, and AccessControl interfaces from OpenZeppelin. You can create the contract yourself using the OpenZeppelin Wizard and enable "Mintable," "Pausable," "URI Storage," and "Access Control → Roles."

Compile your new contract:

npx hardhat build

Step 2: Deploying the Smart Contract and Minting a Token

Create deploy-advanced.ts in your scripts folder:

scripts/deploy-advanced.ts

import { network } from "hardhat";

const { ethers } = await network.connect({
  network: "testnet"
});

async function main() {
  // Get the signer of the tx and address for minting the token
  const [deployer] = await ethers.getSigners();
  console.log("Deploying contract with the account:", deployer.address);

  // The deployer will also be the owner of our NFT contract
  const MyTokenAdvanced = await ethers.getContractFactory(
    "MyTokenAdvanced",
    deployer
  );
  const contract = await MyTokenAdvanced.deploy(
    deployer.address,
    deployer.address,
    "0xc0ffee254729296a45a3885639AC7E10F9d54979"
  );

  await contract.waitForDeployment();

  const address = await contract.getAddress();
  console.log("Contract deployed at:", address);
}

main().catch(console.error);

Note that we are providing three arguments to the MyTokenAdvanced.deploy() function. When we look at the constructor of our smart contract, we can provide the admin, pauser, and minter roles.

constructor(address defaultAdmin, address pauser, address minter)

The deploy-advanced.ts script sets the minter role to an unknown (random) address. This should prevent the deployer account from minting new tokens in the next step. First, let's run the deployer script:

npx hardhat run scripts/deploy-advanced.ts --network testnet

Here's the output of the command:

Deploying contract with the account: 0xA98556A4deeB07f21f8a66093989078eF86faa30
Contract deployed at: 0x5f41411477b506FA32DFe3B73BEE52a3D80B755f

Copy the contract address of your newly deployed contract. Next, create mint-advanced.ts in your scripts folder:

scripts/mint-advanced.ts

import { network } from "hardhat";

const { ethers } = await network.connect({
  network: "testnet"
});

async function main() {
  const [deployer] = await ethers.getSigners();

  // Get the ContractFactory of your MyTokenAdvanced ERC-721 contract
  const MyTokenAdvanced = await ethers.getContractFactory(
    "MyTokenAdvanced",
    deployer
  );

  // Connect to the deployed contract (REPLACE WITH YOUR CONTRACT ADDRESS)
  const contractAddress = "0x6F5F9Ed50140bb9C94246257241Ed5AA5d40A25d";
  const contract = MyTokenAdvanced.attach(contractAddress);

  // Mint a token to ourselves
  const mintTx = await contract.safeMint(
    deployer.address,
    "https://myserver.com/8bitbeard/8bitbeard-tokens/tokens/1"
  );
  const receipt = await mintTx.wait();
  console.log("receipt: ", JSON.stringify(receipt, null, 2));
  const mintedTokenId = receipt?.logs[0].topics[3];
  console.log("Minted token ID:", mintedTokenId);

  // Check the balance of the token
  const balance = await contract.balanceOf(deployer.address);
  console.log("Balance:", balance.toString(), "NFTs");
}

main().catch(console.error);

This contract tries to mint a new token and sets the token URI to https://myserver.com/8bitbeard/8bitbeard-tokens/tokens/1 . This transaction will fail because our deployer account doesn't have the minter permission. Run the script:

npx hardhat run scripts/mint-advanced.ts --network testnet

‼️ Notice minting fails due to incorrect permissions. Let's fix this in the next step.

Step 3: Fixing Permissions, Redeploying, and Minting

Update the minting role to your deployer account by modifying the following line of code in your deploy-advanced.ts script:

scripts/deploy-advanced.ts

const contract = await MyTokenAdvanced.deploy(deployer.address, deployer.address, deployer.address); // Deployer account gets all roles

Now that the deployer account has all the roles, redeploy the contract:

npx hardhat run scripts/deploy-advanced.ts --network testnet

Don't forget to copy the new contract address and update the contractAddress variable in your mint-advanced.ts script with this new address.

Next, execute the minting logic:

npx hardhat run scripts/mint-advanced.ts --network testnet

The new token will be minted with token ID 0 and the corresponding token URI is printed to your terminal.

Step 4: Pausing the Contract

Create a new pause-advanced.ts script and make sure to replace the contractAddress variable with your address:

scripts/pause-advanced.ts

import { network } from "hardhat";

const { ethers } = await network.connect({
  network: "testnet"
});

async function main() {
  const [deployer] = await ethers.getSigners();

  // Get the ContractFactory of your MyTokenAdvanced ERC-721 contract
  const MyTokenAdvanced = await ethers.getContractFactory(
    "MyTokenAdvanced",
    deployer
  );

  // Connect to the deployed contract (REPLACE WITH YOUR CONTRACT ADDRESS)
  const contractAddress = "0x2a35e6532e9e6477205Cc845362EB6e71FcC0F0E";
  const contract = MyTokenAdvanced.attach(contractAddress);

  // Pause the token
  const pauseTx = await contract.pause();
  const receipt = await pauseTx.wait();
  console.log("receipt: ", JSON.stringify(receipt, null, 2));
  console.log("Paused token");

  // Read the paused state
  const pausedState = await contract.paused();
  console.log("Contract paused state is:", pausedState);
}

main().catch(console.error);

The script calls the pause function on your contract. As we have the correct role, the token will be paused, and its paused state will be printed to the terminal. Execute the script:

npx hardhat run scripts/pause-advanced.ts --network testnet

The contract will return true when it is paused. Now, nobody can mint new tokens.

Pausing an ERC-721 contract temporarily disables critical functions, including minting, transferring, and burning tokens. While the contract is paused, users cannot perform these operations, making it particularly useful in emergency scenarios or maintenance periods. However, read operations, such as checking token balances or URIs, are still possible.

Step 5: Transferring NFTs

Create a transfer-advanced.ts script to transfer an NFT to another address. Don't forget to replace the contractAddress with your smart contract address.

scripts/transfer-advanced.ts

async function main() {
  const [deployer] = await ethers.getSigners();
  const MyTokenAdvanced = await ethers.getContractFactory(
    "MyTokenAdvanced",
    deployer
  );

  // Connect to the deployed contract (REPLACE WITH YOUR CONTRACT ADDRESS)
  const contractAddress = "0x11828533C93F8A1e19623343308dFb4a811005dE";
  const contract = await MyTokenAdvanced.attach(contractAddress);

  // Unpause the token
  const unpauseTx = await contract.unpause();
  await unpauseTx.wait();
  console.log("Unpaused token");

  // Read the paused state
  const pausedState = await contract.paused();
  console.log("Contract paused state is:", pausedState);

  // Transfer the token with ID 0
  const transferTx = await contract.transferFrom(
    deployer.address,
    "0x5FbDB2315678afecb367f032d93F642f64180aa3",
    0
  );

  await transferTx.wait();

  const balance = await contract.balanceOf("0x5FbDB2315678afecb367f032d93F642f64180aa3");
  console.log("Balance:", balance.toString(), "NFTs");
}

main().catch(console.error);

This script will first unpause your contract and then transfer the token to a random address 0x5FbDB2315678afecb367f032d93F642f64180aa3 using the transferFrom function on your contract. This function accepts the sender address, receiver address, and the token ID you want to transfer. Next, we check if the account has actually received the token by verifying its balance.

Execute the script to transfer the token:

npx hardhat run scripts/transfer-advanced.ts --network testnet

If the balance for the 0x5FbDB2315678afecb367f032d93F642f64180aa3 account shows 1 , then you've successfully transferred the NFT and completed this tutorial! 🎉

Step 6: Run tests(Optional)

You can find both types of tests in the Hedera-Code-Snippets repository. You will find the following files:

contracts/MyTokenAdvanced.t.sol
test/MyTokenAdvanced.ts

Copy these files and then run the tests:

npx hardhat test

You can also run tests individually with either of these

npx hardhat test solidity
npx hardhat test mocha

Additional Resources

Writer: Michiel, DevRel Engineer

GitHub | LinkedIn

Editor: Luis, Sr Software Developer

GitHub

Editor: Krystal, Technical Writer

GitHub | X

Editor: Kiran, Developer Advocate

GitHub | LinkedIn

PreviousHow to Mint & Burn an ERC-721 Token Using Hardhat and Ethers (Part 1)NextHow to Upgrade an ERC-721 Token with OpenZeppelin UUPS Proxies and Hardhat (Part 3)

Last updated 5 days ago

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Prerequisites

Table of Contents

Video Tutorial

Step 1: Create and Compile the Solidity Contract

Step 2: Deploying the Smart Contract and Minting a Token

Step 3: Fixing Permissions, Redeploying, and Minting

Step 4: Pausing the Contract

Step 5: Transferring NFTs

Step 6: Run tests(Optional)

Additional Resources