Hardhat deployment scripts in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a basic Hardhat deployment script

What will be the output printed to the console when running this Hardhat deployment script?

Blockchain / Solidity

async function main() {
  const [deployer] = await ethers.getSigners();
  console.log('Deploying contracts with the account:', deployer.address);
  const Token = await ethers.getContractFactory('Token');
  const token = await Token.deploy('MyToken', 'MTK', 18, 1000);
  await token.deployed();
  console.log('Token deployed to:', token.address);
}

main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

A SyntaxError: Unexpected token 'await'

B Deploying contracts with the account: 0x... (deployer address)\nToken deployed to: 0x... (contract address)

C Deploying contracts with the account: undefined\nToken deployed to: undefined

D Error: Token contract not found

💡 Hint

Remember that ethers.getSigners() returns an array of accounts and deployer.address is a valid address string.

The script logs the deployer's address and the deployed contract address after deployment. Options B, C, and D are incorrect because the deployer address and contract address are defined, the syntax is correct, and the contract factory is found.

🧠 Conceptual

intermediate

Understanding deployment script parameters

In a Hardhat deployment script, what is the purpose of the line `const Token = await ethers.getContractFactory('Token');`?

A It compiles the Token contract and prepares it for deployment.

B It fetches the deployed Token contract address from the network.

C It deploys the Token contract immediately to the blockchain.

D It imports the Token contract source code as a string.

💡 Hint

Think about what a contract factory does in ethers.js.

The getContractFactory method compiles the contract and returns a factory object that can be used to deploy new instances. It does not deploy immediately or fetch existing addresses.

🔧 Debug

advanced

Identify the error in this deployment script

What error will this Hardhat deployment script produce when run?

Blockchain / Solidity

async function main() {
  const Token = await ethers.getContractFactory('Token')
  const token = Token.deploy('MyToken', 'MTK', 18, 1000)
  await token.deployed()
  console.log('Token deployed to:', token.address)
}

main().catch(console.error);

A ReferenceError: ethers is not defined

B SyntaxError: missing semicolon

C TypeError: token.deployed is not a function

D No error, script runs successfully

💡 Hint

Check if the deploy function is awaited properly.

The deploy() method returns a promise, so it must be awaited. Without await, token is a promise, and token.deployed() is undefined, causing a TypeError.

📝 Syntax

advanced

Correct syntax for deploying with constructor arguments

Which option correctly deploys a contract named 'Crowdsale' with constructor arguments `rate` and `wallet`?

A

const Crowdsale = await ethers.getContractFactory('Crowdsale');
const crowdsale = await Crowdsale.deploy([rate, wallet]);

B

const Crowdsale = ethers.getContractFactory('Crowdsale');
const crowdsale = Crowdsale.deploy(rate, wallet);

C

const Crowdsale = await ethers.getContractFactory('Crowdsale');
const crowdsale = Crowdsale.deploy([rate, wallet]);

D

const Crowdsale = await ethers.getContractFactory('Crowdsale');
const crowdsale = await Crowdsale.deploy(rate, wallet);

💡 Hint

Remember how to pass multiple arguments to a contract constructor in deploy().

Option D correctly awaits getContractFactory and deploys with separate arguments. Options C and D incorrectly pass arguments as an array. Option D misses await and will cause errors.

🚀 Application

expert

Determine the number of deployed contracts

Given this Hardhat deployment script, how many contracts will be deployed to the blockchain after running it?

Blockchain / Solidity

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

  const Token = await ethers.getContractFactory('Token');
  const token = await Token.deploy('MyToken', 'MTK', 18, 1000);
  await token.deployed();

  const Crowdsale = await ethers.getContractFactory('Crowdsale');
  const crowdsale = await Crowdsale.deploy(1, deployer.address, token.address);
  await crowdsale.deployed();

  console.log('Deployment complete');
}

main().catch(console.error);

A 2

B 1

C 3

D 0

💡 Hint

Count each deploy() call that is awaited and completed.

The script deploys two contracts: Token and Crowdsale. Both deploy calls are awaited and completed, so two contracts are deployed.