Finally block in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to ensure the finally block always runs.

Javascript

try {
  console.log('Try block');
} [1] {
  console.log('Catch block');
}

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

Acatch

Bfinally

Celse

Dthrow

Attempts:

3 left

💡 Hint

Common Mistakes

Using catch instead of finally

Forgetting the finally block

Using else which is not valid here

The finally block runs after try and catch blocks, no matter what. Here, to catch errors, catch is needed before finally.

2fill in blank

medium

Complete the code to log a message in the finally block.

Javascript

try {
  throw new Error('Oops');
} catch(e) {
  console.log('Error caught');
} [1] {
  console.log('Always runs');
}

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

Acatch

Bfinally

Celse

Dthrow

Attempts:

3 left

💡 Hint

Common Mistakes

Using catch again instead of finally

Using else which is invalid

Not including finally block

The finally block runs after try and catch, even if an error was thrown.

3fill in blank

hard

Fix the error in the code by completing the block that always runs.

Javascript

try {
  console.log('Start');
} [1] {
  console.log('Cleanup');
}

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

Afinally

Bcatch

Celse

Dcatch(e)

Attempts:

3 left

💡 Hint

Common Mistakes

Using catch without error parameter

Using else which is invalid

Omitting finally block

The finally block runs always, catch needs an error parameter and is for errors only.

4fill in blank

hard

Fill both blanks to create a try-catch-finally structure.

Javascript

try {
  console.log('Trying');
} [1] (error) {
  console.log('Caught error');
} [2] {
  console.log('Always runs');
}

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

Acatch

Bfinally

Cthrow

Delse

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping catch and finally

Using else instead of finally

Omitting catch or finally

catch handles errors, finally runs always after try and catch.

5fill in blank

hard

Fill all three blanks to handle errors and always run cleanup code.

Javascript

try {
  [1]('Hello');
} [2] (e) {
  console.log('Error:', e.message);
} [3] {
  console.log('Done');
}

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

Aconsole.log

Bcatch

Cfinally

Dthrow

Attempts:

3 left

💡 Hint

Common Mistakes

Using throw inside try without catch

Omitting finally block

Using wrong function instead of console.log

console.log prints, catch handles errors, finally runs always after try and catch.

Practice

1.

What is the main purpose of the finally block in JavaScript?

easy

A. To define variables used in try block

B. To run code that always executes after try and catch blocks

C. To catch errors thrown in the try block

D. To skip the catch block if no error occurs

Solution

1. Step 1: Understand try-catch-finally structure

   The try block runs code that might throw errors, catch handles those errors.

2. Step 2: Role of finally block

   The finally block runs code after try and catch, no matter if an error occurred or not.

3. Final Answer:

   To run code that always executes after try and catch blocks -> Option B

4. Quick Check:

   finally always runs = C [OK]

Hint: finally always runs after try/catch, no matter what [OK]

Common Mistakes:

• Thinking finally only runs if there is an error
• Confusing catch and finally blocks
• Believing finally can catch errors

2.

Which of the following is the correct syntax to add a finally block after a try and catch block?

try {
  // code
} catch (e) {
  // handle error
} ??? {
  // cleanup code
}

easy

A. cleanup

B. final

C. finally

D. end

Solution

1. Step 1: Recall JavaScript error handling syntax

   The correct keyword after catch is 'finally' to run code always.

2. Step 2: Check options for correct keyword

   Only 'finally' is valid JavaScript syntax here.

3. Final Answer:

   finally -> Option C

4. Quick Check:

   finally keyword syntax = D [OK]

Hint: finally is the exact keyword after catch for cleanup [OK]

Common Mistakes:

• Using 'final' or 'end' instead of 'finally'
• Omitting the finally block keyword
• Placing finally before catch

3.

What will be the output of this code?

function test() {
  try {
    console.log('Try block');
    return 'Return from try';
  } catch (e) {
    console.log('Catch block');
  } finally {
    console.log('Finally block');
  }
}
console.log(test());

medium

A. Finally block\nReturn from try

B. Try block\nCatch block\nFinally block\nReturn from try

C. Try block\nReturn from try

D. Try block\nFinally block\nReturn from try

Solution

1. Step 1: Trace the try block execution

   It logs 'Try block' and then hits return 'Return from try'.

2. Step 2: Understand finally runs after return

   Even after return, finally runs and logs 'Finally block'. Then function returns.

3. Final Answer:

   Try block\nFinally block\nReturn from try -> Option D

4. Quick Check:

   finally runs after return = A [OK]

Hint: finally runs even after return in try [OK]

Common Mistakes:

• Thinking finally does not run after return
• Expecting catch block to run without error
• Missing the order of console logs

4.

Find the error in this code snippet:

try {
  throw new Error('Oops');
} catch {
  console.log('Caught error');
} finally {
  console.log('Cleanup');
}

medium

A. No error, code runs fine

B. finally block cannot be used without catch parameter

C. throw statement is incorrect

D. Missing error parameter in catch block

Solution

1. Step 1: Check catch block syntax

   Optional catch binding (ES2019+) allows catch {} without parameter. Valid in modern JavaScript.

2. Step 2: Verify execution

   Throws error, catch logs 'Caught error', finally logs 'Cleanup'. No errors.

3. Final Answer:

   No error, code runs fine -> Option A

4. Quick Check:

   catch {} valid = D [OK]

Hint: catch {} valid in modern JS with optional binding [OK]

Common Mistakes:

• Thinking catch always requires parameter
• Believing syntax error without catch param
• Confusing with pre-ES2019 JS

5.

Consider this code:

let result = '';
function test() {
  try {
    result += 'Try';
    throw new Error('Error!');
  } catch (e) {
    result += 'Catch';
    return result;
  } finally {
    result += 'Finally';
  }
}
test();
console.log(result);

What will be printed to the console?

hard

A. TryCatchFinally

B. TryCatch

C. TryFinally

D. Try

Solution

1. Step 1: Trace try block execution

   result becomes 'Try', then error is thrown.

2. Step 2: Catch block runs and appends 'Catch', then returns result ('TryCatch')

   Before returning, finally runs and appends 'Finally' to result.

3. Step 3: Check console.log output

   console.log prints result after finally appended, so 'TryCatchFinally'.

4. Final Answer:

   TryCatchFinally -> Option A

5. Quick Check:

   finally runs before return completes = B [OK]

Hint: finally runs before return completes, modifies variables [OK]

Common Mistakes:

• Assuming return stops finally from running
• Expecting console.log to print before finally modifies result
• Ignoring that finally runs even after return