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.