Deploying to L2 networks in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of L2 Deployment Script

What is the output of this simplified deployment script snippet for an L2 network?

Blockchain / Solidity

const deployContract = async () => {
  const network = 'Optimism';
  const gasLimit = 1500000;
  const contractAddress = '0x123abc';
  console.log(`Deploying to ${network} with gas limit ${gasLimit}`);
  return contractAddress;
};

(async () => {
  const address = await deployContract();
  console.log(`Contract deployed at ${address}`);
})();

A

Deploying to Optimism with gas limit undefined
Contract deployed at 0x123abc

B

Deploying to Optimism with gas limit 1500000
Contract deployed at 0x123abc

C

Deploying to Optimism with gas limit 1500000
Contract deployed at undefined

D SyntaxError: Unexpected token

💡 Hint

Look at the values passed to the console.log statements and the returned contract address.

The function deployContract returns the contract address string, and the logs print the network and gas limit correctly.

🧠 Conceptual

intermediate

Gas Cost Differences in L1 vs L2

Which statement correctly explains why deploying contracts on L2 networks is generally cheaper than on L1?

A L2 networks charge the same gas fees as L1 but process transactions faster.

B L2 networks have higher gas fees because they run on separate blockchains.

C L2 networks batch transactions and use rollups, reducing gas fees compared to L1.

D L2 networks do not require gas fees at all for deployments.

💡 Hint

Think about how L2 networks handle transactions differently from L1.

L2 networks use batching and rollups to reduce the amount of data posted on L1, lowering gas costs.

🔧 Debug

advanced

Identify the Error in L2 Deployment Script

What error will this deployment script produce when run on an L2 network?

Blockchain / Solidity

async function deploy() {
  const provider = new ethers.providers.JsonRpcProvider('https://l2network.rpc');
  const wallet = new ethers.Wallet('0xabc123', provider);
  const factory = new ethers.ContractFactory(abi, bytecode, wallet);
  const contract = await factory.deploy({ gasPrice: 1000000000 });
  await contract.deployed();
  console.log('Contract deployed at:', contract.address);
}
deploy();

A TypeError: gasPrice must be a BigNumber or number, not string

B SyntaxError: Unexpected token 'await'

C ReferenceError: ethers is not defined

D No error, contract deploys successfully

💡 Hint

Check the type of the gasPrice value passed in the deploy options.

The gasPrice option expects a number or BigNumber, but a string was given causing a TypeError.

📝 Syntax

advanced

Correct Syntax for L2 Contract Deployment

Which option shows the correct syntax to deploy a contract on an L2 network using ethers.js with a custom gas limit?

A const contract = await factory.deploy({ gas_limit: 2000000 });

B const contract = await factory.deploy(gasLimit: 2000000);

C const contract = await factory.deploy({ gaslimit: 2000000 });

D const contract = await factory.deploy({ gasLimit: 2000000 });

💡 Hint

Check the correct property name and object syntax for deploy options.

The correct property is 'gasLimit' with capital L inside an object passed to deploy().

🚀 Application

expert

Calculate Total Gas Cost for L2 Deployment

Given a contract deployment on an L2 network with gas limit 1,200,000 and gas price 0.000000002 ETH, what is the total gas cost in ETH?

A 0.0024 ETH

B 2.4 ETH

C 0.0000024 ETH

D 0.024 ETH

💡 Hint

Multiply gas limit by gas price: 1,200,000 * 0.000000002 ETH.

1,200,000 * 0.000000002 = 0.0024 ETH total gas cost.

Practice

1. What is the main benefit of deploying smart contracts to Layer 2 (L2) networks?

easy

A. Increased decentralization over Layer 1

B. More complex contract code execution

C. Faster transactions and lower fees compared to Layer 1

D. Unlimited storage capacity for contracts

Solution

1. Step 1: Understand Layer 2 purpose

   Layer 2 networks are designed to improve blockchain scalability by handling transactions off the main chain.

2. Step 2: Identify benefits of L2

   This results in faster transaction speeds and lower fees compared to Layer 1.

3. Final Answer:

   Faster transactions and lower fees compared to Layer 1 -> Option C

4. Quick Check:

   L2 improves speed and cost [OK]

Hint: L2 means faster and cheaper transactions than L1 [OK]

Common Mistakes:

• Confusing L2 with increased decentralization
• Thinking L2 allows unlimited storage
• Assuming L2 makes contracts more complex

2. Which of the following is the correct syntax to specify an L2 network in a deployment script using Hardhat?

easy

A. "network: 'layer2'" inside the config file

B. "network: 'l1'" inside the deployment script

C. "network: 'mainnet'" inside the config file

D. network: 'layer2'" without quotes in the script

Solution

1. Step 1: Recognize correct network naming

   In Hardhat config, network names are strings and must be quoted.

2. Step 2: Identify L2 network syntax

   Using "network: 'layer2'" inside the config file is the correct way to specify the L2 network.

3. Final Answer:

   "network: 'layer2'" inside the config file -> Option A

4. Quick Check:

   Network names are strings in config [OK]

Hint: Network names must be strings in config files [OK]

Common Mistakes:

• Using unquoted network names causing syntax errors
• Confusing L1 and L2 network names
• Placing network setting inside deployment script instead of config

3. Given this deployment snippet for an L2 network:

const network = 'layer2';
console.log(`Deploying to ${network}`);

What will be the output?

medium

A. Deploying to ${network}

B. Deploying to layer2

C. Deploying to network

D. Error: network not defined

Solution

1. Step 1: Understand template literals

   The backticks and ${} syntax insert variable values into strings.

2. Step 2: Substitute variable value

   Here, ${network} becomes 'layer2', so the output is 'Deploying to layer2'.

3. Final Answer:

   Deploying to layer2 -> Option B

4. Quick Check:

   Template literal inserts variable [OK]

Hint: Backticks with ${} insert variables in strings [OK]

Common Mistakes:

• Confusing template literals with normal quotes
• Expecting literal ${network} output
• Assuming variable is undefined

4. You try to deploy a contract to an L2 testnet but get an error: "Invalid RPC URL". What is the most likely cause?

medium

A. Your private key is invalid

B. The contract code has syntax errors

C. You forgot to compile the contract

D. The RPC URL for the L2 network is missing or incorrect in the config

Solution

1. Step 1: Understand RPC URL role

   The RPC URL connects your deployment tool to the blockchain network.

2. Step 2: Link error to cause

   An "Invalid RPC URL" error means the URL is missing or wrong in the config file.

3. Final Answer:

   The RPC URL for the L2 network is missing or incorrect in the config -> Option D

4. Quick Check:

   Invalid RPC URL means wrong/missing URL [OK]

Hint: Check RPC URL correctness in config first [OK]

Common Mistakes:

• Assuming contract code errors cause RPC URL errors
• Ignoring network config settings
• Not verifying private key separately

5. You want to deploy a contract to an L2 network but keep your private key secure. Which approach is best?

hard

A. Store the private key in environment variables and load it securely

B. Use a public key instead of a private key for deployment

C. Share the private key in the project README for easy access

D. Hardcode the private key in the deployment script

Solution

1. Step 1: Understand private key security

   Private keys must be kept secret to prevent unauthorized access.

2. Step 2: Identify secure storage method

   Using environment variables keeps keys out of code and version control, enhancing security.

3. Final Answer:

   Store the private key in environment variables and load it securely -> Option A

4. Quick Check:

   Env vars keep keys secret [OK]

Hint: Never hardcode keys; use environment variables [OK]

Common Mistakes:

• Hardcoding keys in scripts
• Sharing keys publicly
• Confusing public and private keys