​Hardhat is an Ethereum development environment. It is known for debugging the Solidity code and the explicit error messages. Moreover it has extra nice features such as the interactive JavaScript console and the user defined tasks.

The main objective of this tutorial is to show how to deploy and interact with the Solidity smart contracts on Aurora using Hardhat. This tutorial assumes that you are familiar with Hardhat and the ERC-20 tokens. For more details about the fungible token standard, please refer to the ERC-20 Standard specification.

Installation​

This tutorial assumes that you have Node.js 12+ and Yarn. Please refer to the Yarn installation how-to if you don't yet have the yarn command installed locally.

  • To install the prerequisite packages, clone the examples repository:

git clone https://github.com/aurora-is-near/aurora-examples.git
cd aurora-examples/hardhat/erc20/

  • Add your Aurora Private key (from MetaMask) to .env file and then run yarn :

echo "AURORA_PRIVATE_KEY=YOUR_AURORA_PRIVATE_KEY_HERE" >> .env
yarn install

Deploy ERC-20​

The ERC-20 example is about a native Watermelon token 🍉. You can exchange them into actual Watermelons 🍉🍉🍉. The total supply is 1000000, the minter is the contract deployer address, and the decimals are 0 (One token --> One watermelon).

To deploy the ERC-20 token contract, use the following command:

$ make deploy NETWORK=testnet_aurora
yarn hardhat run scripts/deploy.js --network testnet_aurora
yarn run v1.22.10
Deploying contracts with the account: 0x6A33382de9f73B846878a57500d055B981229ac4
Account balance: 2210010200000000000
WatermelonToken deployed to: 0xD7f2A76F5DA173043E6c61a0A18D835809A07766
✨  Done in 14.96s.

# export the token address
$ export TOKEN_ADDRESS='YOUR OUTPUT FROM DEPLOY (e.g. 0xD7f2A76F5DA173043E6c61a0A18D835809A07766)'

Hardhat Tasks​

Hardhat tasks take care of parsing the values provided for each parameter. It gets the values, performs the type validation and converts them into your desired type.

In this example, we will go through a set of pre-defined Hardhat tasks that uses the Hardhat Runtime Environment (HRE). In order to complete the tutorial, you should use them in the same order:

ETH Balance​

The following Hardhat task uses the Web3 plugin to get the account’s balance:

task("balance", "Prints an account's balance")
  .addParam("account", "The account's address")
  .setAction(async taskArgs => {
    const account = web3.utils.toChecksumAddress(taskArgs.account);
    const balance = await web3.eth.getBalance(account);

    console.log(web3.utils.fromWei(balance, "ether"), "ETH");
  });

To get the ETH balance, use the following command:

npx hardhat balance --network testnet_aurora --account 0x6A33382de9f73B846878a57500d055B981229ac4
2.2100102 ETH

You should notice that --network is a global built-in option (parameter) in Hardhat. We will use it for the following commands as well.

Total Supply​

The following task script gets the total supply of the Watermelon ERC-20 token. First it attaches the token contract, gets the sender address and finally retrieves the total supply by calling totalSupply() method in our ERC-20 contract. The --token address is the ERC-20 contract address.

task("totalSupply", "Total supply of ERC-20 token")
.addParam("token", "Token address")
.setAction(async function ({ token }, { ethers: { getSigners } }, runSuper) {
  const watermelonToken = await ethers.getContractFactory("WatermelonToken")
  const watermelon = watermelonToken.attach(token)
  const [minter] = await ethers.getSigners();
  const totalSupply = (await (await watermelon.connect(minter)).totalSupply()).toNumber()
  console.log(`Total Supply is ${totalSupply}`);
});

To get the totalSupply, use the following command:

$ npx hardhat totalSupply --token $TOKEN_ADDRESS --network testnet_aurora
Total Supply is 1000000

Transfer ERC-20​

The transfer option allows anyone holding an ERC-20 tokens to transfer them to any Ethereum address. In the following script, the minter address will mint (implicitly) and transfer 10 WTM tokens to the spender address:

task("transfer", "ERC-20 transfer")
    .addParam("token", "Token address")
    .addParam("spender", "Spender address")
    .addParam("amount", "Token amount")
    .setAction(async function ({ token, spender, amount }, { ethers: { getSigners } }, runSuper) {
        const watermelonToken = await ethers.getContractFactory("WatermelonToken")
        const watermelon = watermelonToken.attach(token)
        const [minter] = await ethers.getSigners();
        await (await watermelon.connect(minter).transfer(spender, amount)).wait()
        console.log(`${minter.address} has transferred ${amount} to ${spender}`);
    });

To call transfer, use the following command:

$ npx hardhat transfer --token $TOKEN_ADDRESS --amount 10 --spender 0x2531a4D108619a20ACeE88C4354a50e9aC48ecfe --network testnet_aurora
0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266 has transferred 10 tokens to 0x2531a4D108619a20ACeE88C4354a50e9aC48ecfe

BalanceOf ERC-20​

We can prove that the spender has received the exact amount of tokens by calling the balanceOf as shown below:

task("balanceOf", "Total supply of ERC-20 token")
.addParam("token", "Token address")
.addParam("account", "Account address")
.setAction(async function ({ token, account }, { ethers: { getSigners } }, runSuper) {
  const watermelonToken = await ethers.getContractFactory("WatermelonToken")
  const watermelon = watermelonToken.attach(token)
  const [minter] = await ethers.getSigners();
  const balance = (await (await watermelon.connect(minter)).balanceOf(account)).toNumber()
  console.log(`Account ${account} has a total token balance:  ${balance} WTM`);
});

To get the balance, use the following command:

$ npx hardhat balanceOf --token $TOKEN_ADDRESS --account 0x6A33382de9f73B846878a57500d055B981229ac4 --network testnet_aurora
Account 0x6A33382de9f73B846878a57500d055B981229ac4 has a total token balance:  999970 WTM

Approve ERC-20​

In some cases, instead of calling the transfer directly, the sender can approve a specific amount of tokens to be withdrawn from his account to specific recipient address later. This can be done by calling approve then calling transferFrom.

task("approve", "ERC-20 approve")
    .addParam("token", "Token address")
    .addParam("spender", "Spender address")
    .addParam("amount", "Token amount")
    .setAction(async function ({ token, spender, amount }, { ethers: { getSigners } }, runSuper) {
        const watermelonToken = await ethers.getContractFactory("WatermelonToken")
        const watermelon = watermelonToken.attach(token)
        const [sender] = await ethers.getSigners();
        await (await watermelon.connect(sender).approve(spender, amount)).wait()
        console.log(`${sender.address} has approved ${amount} tokens to ${spender}`);
    });

module.exports = {};

To call approve, use the following command:

npx hardhat approve --token $TOKEN_ADDRESS --spender 0x8722C88e82AbCC639148Ab6128Cd63333B2Ad771 --amount 10 --network testnet_aurora
0x6A33382de9f73B846878a57500d055B981229ac4 has approved 10 tokens to 0x8722C88e82AbCC639148Ab6128Cd63333B2Ad771

TransferFrom ERC-20​

After approving the tokens, a recipient can call transferFrom to move the allowance to his account.

task("transferFrom", "ERC-20 transferFrom")
    .addParam("token", "Token address")
    .addParam("sender", "Sender address")
    .addParam("amount", "Token amount")
    .setAction(async function ({ token, sender, amount }, { ethers: { getSigners } }, runSuper) {
        const watermelonToken = await ethers.getContractFactory("WatermelonToken")
        const watermelon = watermelonToken.attach(token)
        const [recipient] = await ethers.getSigners()
        console.log(recipient.address);
        await (await watermelon.connect(recipient).transferFrom(sender, recipient.address, amount)).wait()
        console.log(`${recipient.address} has received ${amount} tokens from ${sender}`)
    });

To call transferFrom, use the following command:

# export the recipient private key
AURORA_PRIVATE_KEY="THE RECIPIENT PRIVATE KEY" npx hardhat transferFrom --token $TOKEN_ADDRESS --sender 0x6A33382de9f73B846878a57500d055B981229ac4  --amount 10 --network testnet_aurora
0x8722C88e82AbCC639148Ab6128Cd63333B2Ad771 has received 10 tokens from 0x6A33382de9f73B846878a57500d055B981229ac4

Checking the balance of 0x8722C88e82AbCC639148Ab6128Cd63333B2Ad771:

npx hardhat balanceOf --token $TOKEN_ADDRESS --account 0x8722C88e82AbCC639148Ab6128Cd63333B2Ad771  --network testnet_aurora
Account 0x8722C88e82AbCC639148Ab6128Cd63333B2Ad771 has a total token balance:  10 WTM

Conclusion​

In this tutorial we deployed an ERC-20 token using Hardhat on the Aurora Testnet, transferred, and approved ERC-20 tokens. Moreover, we added other utility tasks such as getting the total supply, and the account balance. The only difference is we changed the Ethereum Mainnet to the Aurora RPC endpoint.