Catching runtime errors in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of try...catch in JavaScript?

It is used to handle runtime errors gracefully by trying a block of code and catching errors if they occur, preventing the program from crashing.

beginner

What does the catch block receive as its parameter?

The catch block receives the error object that was thrown in the try block, which contains information about the error.

intermediate

How can you throw a custom error in JavaScript?

You can use the throw statement followed by an error object or message, for example: throw new Error('Custom message').

beginner

What happens if an error occurs outside a try...catch block?

The error will be unhandled and usually causes the program to stop or crash, showing an error message in the console.

intermediate

Can you use try...catch to handle asynchronous errors directly?

No, try...catch works for synchronous code. For asynchronous code, you handle errors with catch on promises or use async/await with try...catch.

What keyword starts a block of code where you expect an error might happen?

A try

B catch

C throw

D error

The try block contains code that might throw an error.

Which block runs only if an error occurs in the try block?

A finally

B catch

C throw

D error

The catch block runs when an error is thrown inside the try block.

How do you create a new error to throw?

A try Error('message')

B throw Error('message')

C catch Error('message')

D new Error('message')

You create an error object with new Error('message') and then throw it.

What happens if you don't catch an error?

A The program crashes or stops

B The program continues silently

C The error is ignored

D The error is fixed automatically

Uncaught errors usually cause the program to stop or crash.

Which is the correct way to catch errors from a promise?

A throw promise

B try { promise } catch(error) {}

C promise.catch(error => ...)

D catch(promise)

Promises use the catch method to handle errors asynchronously.

Explain how try...catch helps in handling runtime errors in JavaScript.

Think about what happens when code inside try fails.

Describe how you would handle errors in asynchronous JavaScript code.

Remember that async code needs special handling.