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.

Practice

1. What is the main purpose of a Hardhat deployment script?

easy

A. To test smart contracts locally

B. To write smart contract logic

C. To automate deploying smart contracts to the blockchain

D. To create user interfaces for contracts

Solution

1. Step 1: Understand deployment scripts

   Deployment scripts are used to automate the process of putting smart contracts on the blockchain.

2. Step 2: Differentiate from other tasks

   Writing contract logic, testing, and UI creation are separate tasks from deployment.

3. Final Answer:

   To automate deploying smart contracts to the blockchain -> Option C

4. Quick Check:

   Deployment script = automate deployment [OK]

Hint: Deployment scripts automate contract deployment fast [OK]

Common Mistakes:

• Confusing deployment with contract coding
• Thinking deployment scripts test contracts
• Assuming deployment scripts build UI

2. Which of the following is the correct way to get a contract factory in a Hardhat deployment script?

easy

A. const Contract = await ethers.getContractFactory('MyContract');

B. const Contract = ethers.getContract('MyContract');

C. const Contract = await ethers.deployContract('MyContract');

D. const Contract = ethers.createContractFactory('MyContract');

Solution

1. Step 1: Recall ethers.js method

   The correct method to prepare a contract for deployment is ethers.getContractFactory with await.

2. Step 2: Check syntax correctness

   Options B, C, and D use incorrect method names or miss await keyword.

3. Final Answer:

   const Contract = await ethers.getContractFactory('MyContract'); -> Option A

4. Quick Check:

   Use getContractFactory with await [OK]

Hint: Use await ethers.getContractFactory('Name') to prepare contract [OK]

Common Mistakes:

• Omitting await before getContractFactory
• Using wrong method names like getContract or deployContract
• Confusing contract factory with contract instance

3. Consider this Hardhat deployment script snippet:

const Token = await ethers.getContractFactory('Token');
const token = await Token.deploy();
await token.deployed();

const Sale = await ethers.getContractFactory('Sale');
const sale = await Sale.deploy(token.address);
await sale.deployed();

console.log(sale.address);

What will be printed by console.log(sale.address)?

medium

A. The deployed address of the Token contract

B. An error because token.address cannot be passed

C. Undefined, because sale.address is not set

D. The deployed address of the Sale contract

Solution

1. Step 1: Understand deployment sequence

   The Token contract is deployed first, then its address is passed to Sale contract deployment.

2. Step 2: Identify sale.address value

   After deployment, sale.address holds the Sale contract's blockchain address, which is logged.

3. Final Answer:

   The deployed address of the Sale contract -> Option D

4. Quick Check:

   sale.address = Sale contract address [OK]

Hint: Deployed contract instance has .address property [OK]

Common Mistakes:

• Confusing token.address with sale.address
• Assuming sale.address is undefined before deployment
• Thinking passing token.address causes error

4. Identify the error in this Hardhat deployment script snippet:

const Token = ethers.getContractFactory('Token');
const token = await Token.deploy();
await token.deployed();

medium

A. Missing await before ethers.getContractFactory

B. Missing await before Token.deploy()

C. Missing await before token.deployed()

D. No error, the code is correct

Solution

1. Step 1: Check getContractFactory usage

   ethers.getContractFactory returns a promise, so it needs await.

2. Step 2: Verify other awaits

   Token.deploy() and token.deployed() correctly use await.

3. Final Answer:

   Missing await before ethers.getContractFactory -> Option A

4. Quick Check:

   Always await getContractFactory [OK]

Hint: Always await getContractFactory call [OK]

Common Mistakes:

• Forgetting await on getContractFactory
• Confusing which calls need await
• Assuming deploy() is synchronous

5. You want to deploy two contracts, Token and Marketplace, where Marketplace needs the Token address in its constructor. Which is the correct way to write the deployment script?

hard

A. Deploy Marketplace first, then deploy Token passing marketplace.address

B. Deploy Token first, then deploy Marketplace passing token.address

C. Deploy both contracts simultaneously without passing addresses

D. Deploy Token and Marketplace separately without constructor arguments

Solution

1. Step 1: Understand constructor dependency

   Marketplace requires Token's address, so Token must be deployed first to get its address.

2. Step 2: Deploy in correct order

   Deploy Token, then deploy Marketplace passing token.address to its constructor.

3. Step 3: Reject incorrect options

   Deploying Marketplace first or simultaneously won't provide Token's address; omitting constructor args breaks dependency.

4. Final Answer:

   Deploy Token first, then deploy Marketplace passing token.address -> Option B

5. Quick Check:

   Deploy dependencies first, then dependent contracts [OK]

Hint: Deploy dependencies first, pass addresses to dependent contracts [OK]

Common Mistakes:

• Deploying dependent contract before dependency
• Not passing required constructor arguments
• Deploying contracts simultaneously ignoring dependencies