Hardhat deployment scripts in Blockchain / Solidity

Introduction

Deployment scripts help you put your smart contracts on the blockchain automatically. They save time and avoid mistakes compared to manual deployment.

When you want to deploy a new version of your smart contract to a test or main network.

When you need to deploy multiple contracts in a specific order.

When you want to automate deployment as part of your development workflow.

When you want to keep track of deployed contract addresses easily.

When you want to reuse deployment steps for different networks.

Syntax

Blockchain / Solidity

async function main() {
  const ContractFactory = await ethers.getContractFactory("ContractName");
  const contract = await ContractFactory.deploy();
  await contract.deployed();
  console.log("Contract deployed to:", contract.address);
}

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

The main function is async because deployment takes time.

ethers.getContractFactory prepares the contract for deployment.

Examples

Deploys a token contract with a name, symbol, and initial supply.

Blockchain / Solidity

async function main() {
  const Token = await ethers.getContractFactory("MyToken");
  const token = await Token.deploy("My Token", "MTK", 1000);
  await token.deployed();
  console.log("Token deployed at", token.address);
}

Deploys two contracts where ContractB needs ContractA's address.

Blockchain / Solidity

async function main() {
  const ContractA = await ethers.getContractFactory("ContractA");
  const a = await ContractA.deploy();
  await a.deployed();

  const ContractB = await ethers.getContractFactory("ContractB");
  const b = await ContractB.deploy(a.address);
  await b.deployed();

  console.log("ContractA at", a.address);
  console.log("ContractB at", b.address);
}

Sample Program

This script deploys a simple Greeter contract with a greeting message.

Blockchain / Solidity

async function main() {
  const Greeter = await ethers.getContractFactory("Greeter");
  const greeter = await Greeter.deploy("Hello, Hardhat!");
  await greeter.deployed();
  console.log("Greeter deployed to:", greeter.address);
}

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

Important Notes

Always handle errors in deployment scripts to catch problems early.

Use await contract.deployed() to wait until the contract is fully deployed.

Deployment addresses will be different each time unless you use deterministic deployment.

Summary

Deployment scripts automate putting contracts on the blockchain.

They use async functions and ethers.getContractFactory to prepare contracts.

You can deploy multiple contracts and pass addresses between them.

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