Connecting MetaMask wallet in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Connecting MetaMask wallet

User clicks Connect button

↓

Check if MetaMask is installed

↓

Request account access

↓

User approves or rejects

↓

Get account address

↓

Display connected account

This flow shows how a user connects their MetaMask wallet by clicking a button, the app checks MetaMask presence, requests access, and handles approval or rejection.

Execution Sample

Blockchain / Solidity

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

This code tries to connect to MetaMask and logs the first account if successful.

Execution Table

Step	Action	Check/Request	Result	Next Step
1	User clicks Connect button	N/A	Trigger connectWallet()	Check if MetaMask is installed
2	Check MetaMask presence	window.ethereum exists?	Yes	Request account access
3	Request account access	eth_requestAccounts method called	User approves	Get account address
4	Get account address	accounts array received	accounts[0] = '0xABC123...'	Display connected account
5	Display connected account	Console logs account	Output: Connected account: 0xABC123...	End

💡 Execution stops after displaying the connected account or if MetaMask is not installed or user rejects access.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
window.ethereum	undefined or object	object (MetaMask present)	object	object	object
accounts	undefined	undefined	['0xABC123...']	['0xABC123...']	['0xABC123...']
accounts[0]	undefined	undefined	'0xABC123...'	'0xABC123...'	'0xABC123...'

Key Moments - 3 Insights

What happens if MetaMask is not installed?

At Step 2 in the execution_table, if window.ethereum is undefined, the code alerts the user to install MetaMask and stops further execution.

What if the user rejects the connection request?

At Step 3, if the user rejects, the promise from eth_requestAccounts is rejected and the code should handle this error (now shown in sample), preventing account retrieval.

Why do we use accounts[0]?

At Step 4, accounts is an array of addresses; accounts[0] is the first connected account, which is usually the active wallet address.

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of Step 2?

A User rejects connection

B MetaMask is not installed

C MetaMask is installed (window.ethereum exists)

D Account address received

💡 Hint

Check the 'Result' column in Step 2 of the execution_table.

At which step does the user approve the connection?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Next Step' and 'Result' columns in Step 3 of the execution_table.

If the user rejects the connection request, what should happen?

A The connection process stops without account access

B The app alerts to install MetaMask

C The account address is displayed

D The app automatically retries connection

💡 Hint

Refer to key_moments about user rejection and Step 3 in execution_table.

Concept Snapshot

Connecting MetaMask wallet:
- Check if window.ethereum exists (MetaMask installed)
- Request accounts with 'eth_requestAccounts'
- User approves or rejects connection
- On approval, get accounts array
- Use accounts[0] as connected wallet address

Full Transcript

This visual execution shows how a user connects their MetaMask wallet. First, the user clicks a connect button. The app checks if MetaMask is installed by looking for window.ethereum. If not found, it alerts the user to install MetaMask and stops. If MetaMask is present, the app requests account access using the 'eth_requestAccounts' method. The user can approve or reject this request. If approved, the app receives an array of accounts and uses the first account as the connected wallet address, displaying it. If rejected, the connection stops without access. Variables like window.ethereum and accounts change during these steps, reflecting the connection state.

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