Finally block in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the finally block in JavaScript?

The finally block contains code that always runs after the try and catch blocks, no matter if an error occurred or not.

beginner

When does the code inside a finally block execute?

It executes after the try block finishes, whether an error was thrown or not, and after the catch block if an error was caught.

intermediate

Can the finally block change the return value of a function?

Yes, if the finally block contains a return statement, it overrides any previous return from try or catch.

advanced

What happens if an error is thrown inside the finally block?

The error thrown in finally will replace any previous error or return value, and it will propagate out of the whole try-catch-finally structure.

beginner

Write a simple example of a try-catch-finally block in JavaScript.

try { console.log('Try block runs'); throw new Error('Oops'); } catch (e) { console.log('Catch block runs:', e.message); } finally { console.log('Finally block always runs'); }

When does the finally block run in a try-catch-finally statement?

A Only if an error occurs

B Only if no error occurs

C Always, after try and catch blocks

D Never

The finally block always runs after the try and catch blocks, regardless of errors.

What happens if there is a return statement inside both try and finally blocks?

A The return in <code>finally</code> overrides the one in <code>try</code>

B An error occurs

C Both returns are ignored

D The return in <code>try</code> is used

The finally block's return overrides any previous return from try or catch.

If an error is thrown inside the finally block, what happens?

A The error replaces any previous error or return

B The error is ignored

C The program continues without error

D The error is caught automatically

An error thrown in finally replaces any previous error or return value and propagates out.

Which of these is a correct use of finally?

A To catch errors thrown in <code>try</code>

B To clean up resources like closing files or connections

C To declare variables

D To skip code execution

finally is often used to clean up resources regardless of errors.

Can a finally block exist without a catch block?

A Only in strict mode

B No, <code>catch</code> is required

C Only in older JavaScript versions

D Yes, <code>finally</code> can follow <code>try</code> directly

A finally block can follow a try block without a catch block.

Explain the role of the finally block in JavaScript error handling and when it executes.

Think about what code you want to run no matter what happens in try or catch.

Describe what happens if a return statement is present in both the try and finally blocks.

Consider which return value the function actually sends back.