Multi-chain deployment in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of multi-chain contract deployment script

What is the output of this simplified multi-chain deployment script snippet when deploying a contract to Ethereum and Binance Smart Chain?

Blockchain / Solidity

const chains = ['Ethereum', 'BSC'];
const deployed = {};
for (const chain of chains) {
  deployed[chain] = `Contract deployed on ${chain}`;
}
console.log(deployed);

A {"Ethereum":"Contract deployed on BSC","BSC":"Contract deployed on Ethereum"}

B ["Contract deployed on Ethereum","Contract deployed on BSC"]

C {"Ethereum":"Contract deployed on Ethereum","BSC":"Contract deployed on BSC"}

D SyntaxError: Unexpected token

💡 Hint

Look at how the deployed object keys and values are assigned inside the loop.

The script loops over each chain and assigns a string indicating deployment to the deployed object with the chain name as key. The output is a JSON object with keys 'Ethereum' and 'BSC' and corresponding deployment messages.

🧠 Conceptual

intermediate

Understanding multi-chain deployment benefits

Which of the following is the main benefit of deploying a smart contract on multiple blockchains?

A It makes the contract incompatible with wallets.

B It allows the contract to reach users on different blockchain networks.

C It reduces the contract's security by spreading it thin.

D It increases the contract's gas fees on a single chain.

💡 Hint

Think about why projects want to be on more than one blockchain.

Deploying on multiple blockchains lets the contract interact with users and assets on different networks, increasing reach and usability.

🔧 Debug

advanced

Identify the error in multi-chain deployment script

What error will this multi-chain deployment snippet produce?

Blockchain / Solidity

const chains = ['Ethereum', 'Polygon'];
const deployed = {};
chains.forEach(async (chain) => {
  deployed[chain] = await deployContract(chain);
});
console.log(deployed);

A Output shows empty deployed object {}

B SyntaxError: Unexpected token 'await'

C TypeError: deployContract is not a function

D Output shows deployed contracts correctly

💡 Hint

Consider how async functions inside forEach behave.

The forEach loop does not wait for async callbacks to finish, so console.log runs before deployments complete, showing an empty object.

📝 Syntax

advanced

Correct syntax for multi-chain deployment mapping

Which option correctly creates a mapping of chain names to deployed contract addresses in Solidity?

Blockchain / Solidity

mapping(string => address) public deployedContracts;

A deployedContracts['Ethereum'] = 0x1234567890abcdef1234567890abcdef12345678;

B deployedContracts['Ethereum'] == 0x1234567890abcdef1234567890abcdef12345678;

C deployedContracts['Ethereum'] := 0x1234567890abcdef1234567890abcdef12345678;

D deployedContracts('Ethereum') = 0x1234567890abcdef1234567890abcdef12345678;

💡 Hint

Remember how to assign values to mappings in Solidity.

In Solidity, mapping values are assigned using single equals and square brackets for keys.

🚀 Application

expert

Determine the number of deployed contracts after multi-chain deployment

Given this deployment code snippet, how many contracts are deployed and stored in the 'deployed' object after execution?

Blockchain / Solidity

const chains = ['Ethereum', 'BSC', 'Polygon'];
const deployed = {};
for (let i = 0; i < chains.length; i++) {
  if (chains[i] === 'BSC') continue;
  deployed[chains[i]] = `Contract on ${chains[i]}`;
}
console.log(Object.keys(deployed).length);

A 3

B 0

C 1

D 2

💡 Hint

Check which chain is skipped by the continue statement.

The loop skips 'BSC', so only 'Ethereum' and 'Polygon' get deployed and stored, total 2.