Deploying to L2 networks in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the Layer 2 network RPC URL.

Blockchain / Solidity

const provider = new ethers.providers.JsonRpcProvider('[1]');

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Ahttps://polygon-mumbai.infura.io/v3/YOUR-PROJECT-ID

Bhttps://rinkeby.infura.io/v3/YOUR-PROJECT-ID

Chttps://localhost:8545

Dhttps://mainnet.infura.io/v3/YOUR-PROJECT-ID

Attempts:

3 left

💡 Hint

Common Mistakes

Using a mainnet RPC URL instead of an L2 testnet URL.

Using a local blockchain URL which is not an L2 network.

The Polygon Mumbai testnet is a popular L2 network for deployment, so its RPC URL is used here.

2fill in blank

medium

Complete the code to deploy a contract using the signer connected to the L2 network.

Blockchain / Solidity

const signer = new ethers.Wallet('0xYOUR_PRIVATE_KEY', provider);
const factory = new ethers.ContractFactory(abi, bytecode, [1]);
const contract = await factory.deploy();

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Asigner

Bprovider

Cwallet

Dcontract

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the provider instead of the signer.

Passing an undefined wallet object.

The ContractFactory needs a signer to deploy the contract, so we pass the signer object.

3fill in blank

hard

Fix the error in the code to wait for the contract deployment transaction to be mined on the L2 network.

Blockchain / Solidity

const tx = contract.deployTransaction;
await tx.[1]();

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Aconfirm

Bwait

Cmine

Dsend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'send' which sends a transaction but does not wait.

Using 'mine' or 'confirm' which are not valid methods.

The correct method to wait for a transaction to be mined is wait().

4fill in blank

hard

Fill the blanks to create an object that maps contract names to their deployed addresses on the L2 network, filtering only those with addresses starting with '0x'.

Blockchain / Solidity

const deployedContracts = Object.keys(contracts).reduce((acc, [1]) => {
  if (contracts[[1]].address && contracts[[1]].address.[2]('0x')) {
    acc[[1]] = contracts[[1]].address;
  }
  return acc;
}, {});

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Aname

BstartsWith

Cincludes

Daddress

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'includes' instead of 'startsWith' which checks anywhere in the string.

Using 'address' as the loop variable which is incorrect.

We use 'name' as the variable for keys and 'startsWith' to check the address prefix.

5fill in blank

hard

Fill all three blanks to filter and map contract deployment info: create a new object with keys as uppercased contract names, values as addresses, only for contracts deployed on the L2 network with gas used greater than 100000.

Blockchain / Solidity

const filteredContracts = Object.entries(deployments).reduce((acc, [constName, info]) => {
  if (info.network === 'L2' && info.gasUsed [3] 100000) {
    acc[[1]] = [2];
  }
  return acc;
}, {});

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AconstName.toUpperCase()

Binfo.address

C>

DconstName

Attempts:

3 left

💡 Hint

Common Mistakes

Using the original contract name instead of uppercased.

Using '<' instead of '>' for gasUsed comparison.

We uppercase the contract name for the key, use the address as value, and filter gasUsed greater than 100000.

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