Multi-chain deployment in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a contract named "MultiChain".

Blockchain / Solidity

contract [1] {
    // contract code
}

Drag options to blanks, or click blank then click option'

ADeployChain

BMultiChain

CMultiChainDeploy

DChainMulti

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different contract name that does not match the deployment context.

The contract name must match the intended name for clarity and deployment. "MultiChain" is the correct name here.

2fill in blank

medium

Complete the code to define a function that returns the current chain ID.

Blockchain / Solidity

function getChainId() public view returns (uint256) {
    return [1];
}

Drag options to blanks, or click blank then click option'

Ablock.chainid

Bblock.number

Cmsg.sender

Dtx.origin

Attempts:

3 left

💡 Hint

Common Mistakes

Using block.number which returns the block height, not the chain ID.

Using msg.sender or tx.origin which relate to addresses, not chain info.

The block.chainid returns the current blockchain's chain ID, which is essential for multi-chain deployment.

3fill in blank

hard

Fix the error in the function that sets the chain-specific address mapping.

Blockchain / Solidity

mapping(uint256 => address) public chainAddresses;

function setAddress(uint256 chainId, address addr) public {
    chainAddresses[[1]] = addr;
}

Drag options to blanks, or click blank then click option'

AchainId

BchainAddresses

Cmsg.sender

Daddr

Attempts:

3 left

💡 Hint

Common Mistakes

Using the address or the mapping itself as the key instead of the chain ID.

The mapping key should be the chainId parameter to correctly store the address for that chain.

4fill in blank

hard

Fill both blanks to complete the function that returns the address for the current chain.

Blockchain / Solidity

function getAddress() public view returns (address) {
    uint256 currentChain = [1];
    return chainAddresses[[2]];
}

Drag options to blanks, or click blank then click option'

Ablock.chainid

Bmsg.sender

CcurrentChain

Dtx.origin

Attempts:

3 left

💡 Hint

Common Mistakes

Using msg.sender or tx.origin instead of the chain ID.

Using block.chainid directly in the return statement without storing it first.

The function first gets the current chain ID using block.chainid and then returns the address stored for that chain using the variable currentChain.

5fill in blank

hard

Fill all three blanks to complete the multi-chain deployment contract with initialization.

Blockchain / Solidity

contract MultiChain {
    mapping(uint256 => address) public chainAddresses;

    constructor(address [1]) {
        uint256 chainId = [2];
        chainAddresses[chainId] = [3];
    }
}

Drag options to blanks, or click blank then click option'

AinitialAddress

Bblock.chainid

Dmsg.sender

Attempts:

3 left

💡 Hint

Common Mistakes

Using msg.sender instead of the passed address parameter.

Not using block.chainid to get the chain ID.

Mixing up variable names in the constructor.

The constructor takes an initialAddress parameter, gets the current chain ID with block.chainid, and sets the mapping for that chain to the initial address.

Practice

1.

What is the main benefit of multi-chain deployment in blockchain apps?

easy

A. It allows the app to run on multiple blockchains to reach more users.

B. It makes the app run faster on a single blockchain.

C. It reduces the app's code size significantly.

D. It guarantees zero transaction fees on all blockchains.

Solution

1. Step 1: Understand multi-chain deployment purpose

   Multi-chain deployment means putting your app on many blockchains.

2. Step 2: Identify the main benefit

   This helps reach more users and keeps the app working if one chain has issues.

3. Final Answer:

   It allows the app to run on multiple blockchains to reach more users. -> Option A

4. Quick Check:

   Multi-chain deployment = reach more users [OK]

Hint: Multi-chain means many blockchains, so more users [OK]

Common Mistakes:

• Thinking it only speeds up the app
• Believing it reduces code size
• Assuming it removes all fees

2.

Which of the following is the correct way to specify multiple blockchain networks in a deployment config file?

{
  "networks": ["ethereum", "polygon", "binance"]
}

easy

A. { "networks": ["ethereum", "polygon", "binance"] }

B. { networks = [ethereum, polygon, binance] }

C. { networks: (ethereum, polygon, binance) }

D. { "networks": "ethereum, polygon, binance" }

Solution

1. Step 1: Recognize JSON array syntax

   JSON arrays use square brackets [] with comma-separated strings in quotes.

2. Step 2: Match correct syntax

   { "networks": ["ethereum", "polygon", "binance"] } correctly uses ["ethereum", "polygon", "binance"] as an array of strings.

3. Final Answer:

   { "networks": ["ethereum", "polygon", "binance"] } -> Option A

4. Quick Check:

   JSON arrays use [] with quoted strings [OK]

Hint: JSON arrays use square brackets and quotes for strings [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Missing quotes around strings
• Using equals sign instead of colon

3.

Consider this simplified deployment script snippet for multi-chain:

const chains = ["eth", "bsc"];
for (const chain of chains) {
  deployContract(chain);
}

function deployContract(chain) {
  console.log(`Deploying on ${chain}`);
}

What will be the output when this code runs?

medium

A. Deploying on eth,bsc

B. Deploying on eth\nDeploying on bsc

C. Deploying on chains

D. Error: deployContract is not defined

Solution

1. Step 1: Understand the loop over chains array

   The for loop runs twice: once with 'eth', once with 'bsc'.

2. Step 2: Check deployContract output

   Each call prints 'Deploying on ' plus the chain name.

3. Final Answer:

   Deploying on eth\nDeploying on bsc -> Option B

4. Quick Check:

   Loop prints each chain name separately [OK]

Hint: Loop prints each chain separately with deployContract [OK]

Common Mistakes:

• Thinking it prints the whole array as one string
• Expecting an error due to function scope
• Confusing variable names

4.

Find the error in this multi-chain deployment snippet:

const chains = ["eth", "polygon"];
chains.forEach(chain => {
  deploy(chain);
});

function deploy(network) {
  console.log("Deploying to " + network);
}

medium

A. The deploy function name conflicts with a reserved word.

B. The forEach method is not valid on arrays.

C. There is no error; the code runs correctly.

D. The function deploy is called before it is defined.

Solution

1. Step 1: Check function hoisting in JavaScript

   Function declarations are hoisted, so deploy can be called before definition.

2. Step 2: Verify forEach usage

   forEach is valid on arrays and used correctly here.

3. Final Answer:

   There is no error; the code runs correctly. -> Option C

4. Quick Check:

   Function hoisting and forEach usage are correct [OK]

Hint: Function declarations are hoisted; forEach works on arrays [OK]

Common Mistakes:

• Thinking function must be defined before use
• Believing forEach is invalid on arrays
• Assuming deploy is a reserved word

5.

You want to deploy a smart contract on Ethereum, Polygon, and Binance Smart Chain using a script. Which approach best ensures your deployment is safe and works on all chains?

1. Use test networks for each chain first.
2. Deploy directly to mainnets without testing.
3. Write separate scripts for each chain with no shared code.
4. Ignore chain-specific gas fees and settings.

hard

A. Ignore gas fees and settings; they are the same everywhere.

B. Deploy directly to mainnets to save time.

C. Write separate scripts for each chain without sharing code.

D. Use test networks for each chain first to verify deployment.

Solution

1. Step 1: Understand importance of test networks

   Test networks simulate real chains safely to catch errors before mainnet deployment.

2. Step 2: Evaluate deployment best practices

   Deploying directly risks loss; ignoring gas fees causes failures; separate scripts increase errors.

3. Final Answer:

   Use test networks for each chain first to verify deployment. -> Option D

4. Quick Check:

   Testing on testnets ensures safe multi-chain deployment [OK]

Hint: Always test on testnets before mainnet deployment [OK]

Common Mistakes:

• Skipping tests and deploying directly
• Ignoring chain-specific settings
• Duplicating code unnecessarily