Finally block in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of finally block with return

What is the output of this JavaScript code?

function test() {
  try {
    return 'try';
  } finally {
    return 'finally';
  }
}
console.log(test());

Javascript

function test() {
  try {
    return 'try';
  } finally {
    return 'finally';
  }
}
console.log(test());

A try

B undefined

C finally

D Error

💡 Hint

Remember that the finally block runs after try and can override return values.

In JavaScript, if both try and finally blocks have return statements, the return in finally overrides the one in try.

❓ Predict Output

intermediate

Finally block execution with thrown error

What will be logged to the console?

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

Javascript

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

A Cleanup\nError: Oops

B No output

C Error: Oops

D Cleanup

💡 Hint

The finally block runs even if an error is thrown.

The finally block runs and logs 'Cleanup'. The error is thrown but not caught, so it appears as an uncaught error after the log.

❓ Predict Output

advanced

Return value with try, catch, and finally

What is the output of this code?

function example() {
  try {
    throw 'error';
  } catch (e) {
    return 'catch';
  } finally {
    return 'finally';
  }
}
console.log(example());

Javascript

function example() {
  try {
    throw 'error';
  } catch (e) {
    return 'catch';
  } finally {
    return 'finally';
  }
}
console.log(example());

A catch

B finally

C undefined

D error

💡 Hint

Consider which return statement takes priority.

The finally block's return overrides the catch block's return, so 'finally' is returned.

❓ Predict Output

advanced

Finally block with thrown error and catch

What will be the output?

try {
  throw 'fail';
} catch (e) {
  console.log('Caught:', e);
  throw 'new fail';
} finally {
  console.log('Finally block');
}

Javascript

try {
  throw 'fail';
} catch (e) {
  console.log('Caught:', e);
  throw 'new fail';
} finally {
  console.log('Finally block');
}

A Finally block

B Finally block\nCaught: fail

C Caught: fail

D Caught: fail\nFinally block

💡 Hint

The finally block runs after catch, even if catch throws again.

The catch block logs 'Caught: fail' and throws a new error. The finally block runs and logs 'Finally block'.

🧠 Conceptual

expert

Effect of finally on thrown error propagation

Consider this code:

function f() {
  try {
    throw 'error';
  } finally {
    return 'finally';
  }
}

try {
  console.log(f());
} catch (e) {
  console.log('Caught:', e);
}

What will be printed to the console?

A finally

B Error: error

C undefined

D Caught: error

💡 Hint

A return in finally overrides thrown errors.

The throw in try is overridden by the return in finally, so no error propagates and 'finally' is printed.

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