Connecting MetaMask wallet in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if MetaMask is installed.

Blockchain / Solidity

if (typeof window.ethereum [1] 'undefined') {
  console.log('MetaMask is installed!');
} else {
  console.log('Please install MetaMask.');
}

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

A===

B!==

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of !== causes wrong detection.

Using = instead of comparison operator.

We use !== 'undefined' to check if MetaMask (window.ethereum) exists.

2fill in blank

medium

Complete the code to request account access from MetaMask.

Blockchain / Solidity

const accounts = await window.ethereum.request({ method: '[1]' });

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

Aeth_requestAccounts

Beth_accounts

Ceth_getBalance

Deth_sendTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'eth_accounts' only returns accounts if already connected.

Using 'eth_getBalance' is for balance, not accounts.

The method 'eth_requestAccounts' asks MetaMask to connect and provide accounts.

3fill in blank

hard

Fix the error in the code to handle MetaMask connection errors.

Blockchain / Solidity

try {
  const accounts = await window.ethereum.request({ method: 'eth_requestAccounts' });
  console.log('Connected account:', [1]);
} catch (error) {
  console.error('User rejected the request');
}

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

Aaccount[0]

Baccount

Caccounts

Daccounts[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'account' instead of 'accounts'.

Using 'accounts' directly prints the array, not the first account.

The accounts variable is an array; the first account is accounts[0].

4fill in blank

hard

Fill both blanks to listen for account changes and log the new account.

Blockchain / Solidity

window.ethereum.on('[1]', (accounts) => {
  console.log('Account changed to:', [2]);
});

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

AaccountsChanged

BchainChanged

Caccounts[0]

Daccounts

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'chainChanged' event instead of 'accountsChanged'.

Logging the whole accounts array instead of the first account.

The event 'accountsChanged' fires when user switches accounts. The new account is accounts[0].

5fill in blank

hard

Fill all three blanks to create a function that connects MetaMask and returns the first account.

Blockchain / Solidity

async function connectMetaMask() {
  if (typeof window.ethereum [1] 'undefined') {
    try {
      const accounts = await window.ethereum.request({ method: '[2]' });
      return [3];
    } catch (error) {
      console.error('Connection failed');
      return null;
    }
  } else {
    console.log('MetaMask not installed');
    return null;
  }
}

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

A!==

B===

Ceth_requestAccounts

Daccounts[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Using === instead of !== for existence check.

Using wrong method name for request.

Returning the whole accounts array instead of first account.

Check if window.ethereum is not undefined, request accounts with 'eth_requestAccounts', and return the first account.

Practice

1. What does window.ethereum represent in a web page when MetaMask is installed?

easy

A. A browser setting to enable cookies

B. An object injected by MetaMask to interact with the Ethereum blockchain

C. A method to create a new Ethereum wallet

D. A function to send transactions automatically

Solution

1. Step 1: Understand MetaMask injection

   MetaMask injects window.ethereum into the browser to allow web pages to communicate with the Ethereum blockchain.

2. Step 2: Identify the role of window.ethereum

   This object provides methods to request accounts, send transactions, and listen to blockchain events.

3. Final Answer:

   An object injected by MetaMask to interact with the Ethereum blockchain -> Option B

4. Quick Check:

   window.ethereum = MetaMask's injected object [OK]

Hint: Remember: window.ethereum is MetaMask's bridge to Ethereum [OK]

Common Mistakes:

• Thinking window.ethereum is a function
• Confusing it with wallet creation
• Assuming it's a browser setting

2. Which of the following is the correct way to request account access from MetaMask in JavaScript?

easy

A. window.ethereum.getAccounts()

B. window.ethereum.enable()

C. window.ethereum.request({ method: 'eth_requestAccounts' })

D. window.ethereum.connect()

Solution

1. Step 1: Identify the current recommended method

   The modern and recommended way to request accounts is using window.ethereum.request with the method eth_requestAccounts.

2. Step 2: Compare options

   window.ethereum.enable() (enable()) is deprecated. Options C and D are not valid MetaMask methods.

3. Final Answer:

   window.ethereum.request({ method: 'eth_requestAccounts' }) -> Option C

4. Quick Check:

   Use request with eth_requestAccounts to connect [OK]

Hint: Use window.ethereum.request with 'eth_requestAccounts' [OK]

Common Mistakes:

• Using deprecated enable() method
• Calling non-existent getAccounts() or connect()
• Not passing method as an object

3. What will the following code output if the user rejects the MetaMask connection request?

async function connect() {
  try {
    const accounts = await window.ethereum.request({ method: 'eth_requestAccounts' });
    console.log('Connected:', accounts[0]);
  } catch (error) {
    console.log('Error:', error.message);
  }
}
connect();

medium

A. Connected: 0x123... (first account address)

B. Error: window.ethereum is undefined

C. No output

D. Error: User rejected the request.

Solution

1. Step 1: Understand the try-catch block

   The code tries to request accounts. If the user rejects, the promise rejects and control goes to catch block.

2. Step 2: Identify the error message on rejection

   When user rejects, MetaMask throws an error with message like 'User rejected the request.'

3. Final Answer:

   Error: User rejected the request. -> Option D

4. Quick Check:

   User rejection triggers catch with error message [OK]

Hint: User rejection triggers catch block with error message [OK]

Common Mistakes:

• Assuming accounts array is returned on rejection
• Not handling promise rejection
• Expecting no output on rejection

4. Identify the error in this code snippet that tries to connect MetaMask wallet:

async function connectWallet() {
  const accounts = window.ethereum.request('eth_requestAccounts');
  console.log(accounts[0]);
}
connectWallet();

medium

A. Missing await before window.ethereum.request call

B. Incorrect method name, should be 'requestAccounts'

C. window.ethereum.request does not exist

D. accounts is not an array

Solution

1. Step 1: Check the request call usage

   window.ethereum.request returns a Promise, so it must be awaited or handled with then().

2. Step 2: Identify missing await

   The code calls request without await, so accounts is a Promise, not an array, causing accounts[0] to be undefined.

3. Final Answer:

   Missing await before window.ethereum.request call -> Option A

4. Quick Check:

   Async calls need await to get resolved value [OK]

Hint: Always await async calls like window.ethereum.request [OK]

Common Mistakes:

• Forgetting await on async calls
• Passing method as string instead of object
• Assuming request returns array directly

5. You want to connect a MetaMask wallet and display the connected account or an error message if MetaMask is not installed. Which code snippet correctly handles both cases?

async function connect() {
  if (window.ethereum) {
    try {
      const accounts = await window.ethereum.request({ method: 'eth_requestAccounts' });
      console.log('Connected account:', accounts[0]);
    } catch (error) {
      console.log('Connection error:', error.message);
    }
  } else {
    console.log('MetaMask is not installed');
  }
}
connect();

hard

A. Correctly checks for MetaMask and handles connection and errors

B. Fails to check if window.ethereum exists before requesting accounts

C. Does not handle user rejection errors

D. Uses deprecated enable() method instead of request()

Solution

1. Step 1: Check for MetaMask presence

   The code correctly checks if window.ethereum exists before trying to connect.

2. Step 2: Handle connection and errors properly

   It uses try-catch to handle user rejection or other errors and logs appropriate messages.

3. Final Answer:

   Correctly checks for MetaMask and handles connection and errors -> Option A

4. Quick Check:

   Check existence + try-catch = robust connection [OK]

Hint: Always check window.ethereum before connecting [OK]

Common Mistakes:

• Not checking if MetaMask is installed
• Ignoring errors from user rejection
• Using deprecated methods