Transaction confirmation handling in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a transaction is confirmed.

Blockchain / Solidity

if transaction.status == [1]:
    print("Transaction confirmed")

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

A"confirmed"

B"pending"

C"failed"

D"unknown"

Attempts:

3 left

💡 Hint

Common Mistakes

Using "pending" instead of "confirmed".

Checking for "failed" status.

The transaction status must be "confirmed" to indicate it is successfully processed.

2fill in blank

medium

Complete the code to wait for 3 confirmations before proceeding.

Blockchain / Solidity

while transaction.confirmations < [1]:
    wait_for_new_block()

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

A0

B1

C6

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 confirmation which might be unsafe.

Using 0 which means no wait.

Waiting for 3 confirmations is a common practice to ensure transaction finality.

3fill in blank

hard

Fix the error in the code to correctly check transaction finality.

Blockchain / Solidity

if transaction.confirmations [1] 3:
    print("Transaction is final")

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

A>=

B==

C<

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' which checks for fewer confirmations.

Using '==' which is too strict.

Transaction is final when confirmations are greater than or equal to 3.

4fill in blank

hard

Fill both blanks to create a dictionary of transaction IDs with their confirmation counts greater than 2.

Blockchain / Solidity

confirmed_txs = {tx.id: tx[1] for tx in transactions if tx.confirmations [2] 2}

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

A.confirmations

B>

C>=

D.status

Attempts:

3 left

💡 Hint

Common Mistakes

Using '.status' instead of '.confirmations'.

Using '>=' instead of '>'.

We want the confirmation count for each transaction and only those with more than 2 confirmations.

5fill in blank

hard

Fill all three blanks to filter transactions with status 'confirmed' and confirmations at least 3, then map their IDs to confirmation counts.

Blockchain / Solidity

final_txs = {tx[1]: tx[2] for tx in transactions if tx.status == [3] and tx.confirmations >= 3}

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

A.id

B.confirmations

C"confirmed"

D"pending"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pending' instead of 'confirmed' for status.

Mixing up keys and values in the dictionary.

This code creates a dictionary with transaction IDs as keys and their confirmation counts as values, only for confirmed transactions with at least 3 confirmations.

Practice

1. What does transaction confirmation mean in blockchain?

easy

A. It means the transaction is deleted from the blockchain.

B. It means the transaction is reversed by the user.

C. It means the transaction is pending and not yet sent.

D. It means the transaction is safely recorded on the blockchain.

Solution

1. Step 1: Understand transaction confirmation meaning

   Transaction confirmation means the blockchain network has recorded the transaction securely.

2. Step 2: Compare options with definition

   Only It means the transaction is safely recorded on the blockchain. correctly states that confirmation means safe recording on the blockchain.

3. Final Answer:

   It means the transaction is safely recorded on the blockchain. -> Option D

4. Quick Check:

   Transaction confirmation = safe recording [OK]

Hint: Confirmation means transaction is securely recorded [OK]

Common Mistakes:

• Confusing confirmation with transaction pending state
• Thinking confirmation means deletion or reversal
• Assuming confirmation means user approval

2. Which of the following is the correct way to wait for a transaction confirmation in JavaScript using async/await?

easy

A. await transaction.confirm();

B. transaction.wait();

C. await transaction.wait();

D. transaction.confirm();

Solution

1. Step 1: Identify correct async syntax

   To wait for a promise in JavaScript, use await before the async function call.

2. Step 2: Match function name for confirmation

   The standard method to wait for transaction confirmation is wait(), not confirm().

3. Final Answer:

   await transaction.wait(); -> Option C

4. Quick Check:

   Use await with wait() to confirm transaction [OK]

Hint: Use await with wait() method to confirm transaction [OK]

Common Mistakes:

• Forgetting to use await causing unresolved promises
• Using wrong method name like confirm()
• Calling wait() without await leading to no pause

3. What will be the output of this JavaScript code snippet?

async function confirmTx(tx) {
  const receipt = await tx.wait();
  return receipt.confirmations;
}

const fakeTx = {
  wait: () => Promise.resolve({ confirmations: 3 })
};

confirmTx(fakeTx).then(console.log);

medium

A. 3

B. Promise {<pending>}

C. undefined

D. Error: wait is not a function

Solution

1. Step 1: Understand async function behavior

   The function confirmTx awaits tx.wait() which resolves to an object with confirmations: 3.

2. Step 2: Return and log confirmations

   The function returns receipt.confirmations which is 3, and then(console.log) prints 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Await wait() returns confirmations = 3 [OK]

Hint: Await returns resolved value, then log confirmations [OK]

Common Mistakes:

• Expecting Promise instead of resolved value
• Confusing property name confirmations
• Missing await causing Promise output

4. Identify the error in this code snippet for waiting transaction confirmation:

async function waitForConfirmation(tx) {
  const receipt = tx.wait();
  console.log(receipt.confirmations);
}

waitForConfirmation(transaction);

medium

A. Missing await before tx.wait()

B. Incorrect property name confirmations

C. Function should not be async

D. console.log should be outside the function

Solution

1. Step 1: Check async call usage

   The function calls tx.wait() which returns a Promise, but does not use await.

2. Step 2: Understand consequences of missing await

   Without await, receipt is a Promise object, so receipt.confirmations is undefined.

3. Final Answer:

   Missing await before tx.wait() -> Option A

4. Quick Check:

   Always await async calls to get resolved value [OK]

Hint: Always await async calls to get actual result [OK]

Common Mistakes:

• Not using await with async functions
• Assuming Promise has properties directly
• Misplacing console.log inside async function

5. You want to wait for at least 5 confirmations before proceeding with a transaction. Which code snippet correctly implements this logic?

hard

A. const receipt = await tx.wait(5); if(receipt.confirmations < 5) { proceed(); }

B. const receipt = await tx.wait(5); if(receipt.confirmations >= 5) { proceed(); }

C. const receipt = await tx.wait(3); if(receipt.confirmations >= 5) { proceed(); }

D. const receipt = await tx.wait(); if(receipt.confirmations == 5) { proceed(); }

Solution

1. Step 1: Use wait() with confirmation count

   Calling tx.wait(5) waits until at least 5 confirmations are reached.

2. Step 2: Check confirmations before proceeding

   Check if receipt.confirmations >= 5 to ensure safe confirmation before calling proceed().

3. Final Answer:

   const receipt = await tx.wait(5); if(receipt.confirmations >= 5) { proceed(); } -> Option B

4. Quick Check:

   wait(5) ensures 5 confirmations before proceed [OK]

Hint: Use wait(5) and check confirmations >= 5 before proceed [OK]

Common Mistakes:

• Waiting fewer confirmations than needed
• Checking for exact 5 instead of >= 5
• Proceeding when confirmations are less than required