Connecting MetaMask wallet in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output when MetaMask is not installed?

Consider this code snippet that tries to connect to MetaMask. What will it print if MetaMask is not installed in the browser?

Blockchain / Solidity

async function connectWallet() {
  if (typeof window.ethereum === 'undefined') {
    console.log('MetaMask is not installed');
    return;
  }
  try {
    const accounts = await window.ethereum.request({ method: 'eth_requestAccounts' });
    console.log('Connected account:', accounts[0]);
  } catch (error) {
    console.log('User rejected the connection');
  }
}

connectWallet();

A MetaMask is not installed

B TypeError: window.ethereum.request is not a function

C User rejected the connection

D Connected account: 0x123...abc

💡 Hint

Check what happens if window.ethereum is undefined.

If MetaMask is not installed, window.ethereum is undefined, so the code prints 'MetaMask is not installed' and returns early.

❓ Predict Output

intermediate

What happens if user rejects MetaMask connection request?

Given this code to connect MetaMask wallet, what will be printed if the user rejects the connection request?

Blockchain / Solidity

async function connectWallet() {
  if (!window.ethereum) {
    console.log('MetaMask not found');
    return;
  }
  try {
    const accounts = await window.ethereum.request({ method: 'eth_requestAccounts' });
    console.log('Connected:', accounts[0]);
  } catch (error) {
    console.log('User rejected the connection');
  }
}

connectWallet();

A MetaMask not found

B Connected: 0xabc123...

C User rejected the connection

D SyntaxError: Unexpected token

💡 Hint

What does the catch block do?

If the user rejects the connection, the request promise throws an error caught by catch, which logs 'User rejected the connection'.

🔧 Debug

advanced

Why does this MetaMask connection code fail with a TypeError?

Look at this code snippet. It throws a TypeError: window.ethereum.request is not a function. What is the cause?

Blockchain / Solidity

async function connect() {
  if (!window.ethereum) {
    console.log('No MetaMask');
    return;
  }
  try {
    const accounts = await window.ethereum.send('eth_requestAccounts');
    console.log('Account:', accounts[0]);
  } catch (e) {
    console.log('Error:', e.message);
  }
}

connect();

A window.ethereum.send is deprecated; use window.ethereum.request instead

B window.ethereum is undefined, so request method is missing

C The method 'eth_requestAccounts' is invalid

D Missing await keyword before window.ethereum.send

💡 Hint

Check the MetaMask API for the correct method to request accounts.

The send method is deprecated and may not exist or behave differently. The correct method is window.ethereum.request with the method name.

🧠 Conceptual

advanced

What is the purpose of 'eth_requestAccounts' method in MetaMask?

In MetaMask integration, what does calling window.ethereum.request({ method: 'eth_requestAccounts' }) do?

A It sends a transaction to transfer Ether from the user to the dApp

B It disconnects the user's wallet from the dApp

C It fetches the current balance of the user's wallet

D It requests the user to connect their wallet and returns an array of their account addresses

💡 Hint

Think about what connecting a wallet means.

The method asks the user to approve connection and returns their wallet addresses if approved.

❓ Predict Output

expert

What is the output of this MetaMask connection code with event listener?

This code connects to MetaMask and listens for account changes. What will it print if the user switches to account '0xABC123' after connection?

Blockchain / Solidity

async function connectAndListen() {
  if (!window.ethereum) {
    console.log('MetaMask missing');
    return;
  }
  try {
    const accounts = await window.ethereum.request({ method: 'eth_requestAccounts' });
    console.log('Connected:', accounts[0]);
    window.ethereum.on('accountsChanged', (newAccounts) => {
      console.log('Account changed to:', newAccounts[0]);
    });
  } catch {
    console.log('Connection failed');
  }
}

connectAndListen();

// Simulate user switching account after 2 seconds
setTimeout(() => {
  window.ethereum.emit('accountsChanged', ['0xABC123']);
}, 2000);

A

Connected: 0xABC123
Account changed to: 0xOriginal

B

Connected: 0xOriginal
Account changed to: 0xABC123

C MetaMask missing

D Connection failed

💡 Hint

The event listener logs when accounts change after initial connection.

First it logs the original connected account, then when the event fires, it logs the new account.