Practice: Exception Handling

Which keyword starts a block where code that might throw an error is placed?

• Throw

• Catch

• Finally

• Try

Answer explanation

The try block wraps risky code so errors can be caught. Catch handles errors after they are thrown, not before.

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Blooms Level: Remember

What value does the catch block receive as its parameter?

• A numeric status code

• An error object

• A boolean flag value

• A raw stack trace string

Answer explanation

Catch receives an Error object with properties like message and name. A stack trace string is just one property of that object, not the parameter itself.

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Blooms Level: Remember

A developer needs cleanup code to run after a try block, even if catch also runs. Where does it go?

• In the catch block

• In the try block

• In the finally block

• In a throw statement

Answer explanation

Finally executes after try and catch complete, making it the right place for cleanup like closing files or resetting UI state.

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Blooms Level: Apply

Which keyword raises a custom error from inside a function?

• Raise

• Error

• Throw

• Catch

Answer explanation

Throw signals an error and stops normal execution. Error is the constructor used with throw, not the keyword that raises it.

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Blooms Level: Remember

Which TWO statements about try-catch-finally are correct? (Select all that apply)

• Try must be paired with catch, finally, or both

• Errors thrown in try skip remaining try statements

• Catch only runs when an error is thrown

• Finally runs only when no error occurs

• Throw can only appear inside a catch block

Answer explanation

Catch fires only on errors, and try requires at least one of catch or finally. Finally runs in both cases, and throw is allowed anywhere.

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Blooms Level: Analyze

What happens to code after a throw statement in the same try block?

• It executes normally

• It runs after finally

• It is skipped entirely

• It runs only if catch is absent

Answer explanation

Throw immediately exits the current block, so later statements in try are skipped. Control jumps to the matching catch block.

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Blooms Level: Understand

Which try-catch-finally structure is syntactically valid in JavaScript?

• Catch block without try

• Try block without catch or finally

• Finally block without try

• Try block followed only by finally

Answer explanation

Try requires catch, finally, or both. A standalone catch or finally without try causes a syntax error.

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Blooms Level: Remember

Which TWO scenarios are appropriate uses of throw? (Select all that apply)

• Ending a normal loop iteration

• Rejecting input that fails validation

• Signaling invalid function arguments

• Returning a value from a function

• Logging a debug message to the console

Answer explanation

Throw is for exceptional conditions like failed validation or invalid arguments. Loops use break or continue, returns use return, and logging uses console methods.

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Blooms Level: Apply

What is the primary benefit of using try-catch instead of letting errors propagate?

• It prevents the script from crashing unexpectedly

• It automatically fixes bugs in the code

• It speeds up overall script execution

• It eliminates the need for unit testing

Answer explanation

Catching errors lets the program continue or fail gracefully instead of crashing. It does not improve speed or replace testing.

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Blooms Level: Understand

Which line correctly throws a new Error object with a message in JavaScript?

• Throw 'Invalid input';

• Throw new Error('Invalid input');

• Catch new Error('Invalid input');

• Error.throw('Invalid input');

Answer explanation

throw new Error('message') is the standard pattern and preserves the stack trace. Throwing a raw string works but loses Error object properties.

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Blooms Level: Remember