Try-catch for synchronous errors in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a try-catch block in Node.js?

A try-catch block is used to handle errors that happen during the execution of synchronous code. It lets the program continue running instead of crashing.

beginner

Which type of errors can be caught by a try-catch block?

Try-catch blocks catch synchronous errors only. They do not catch errors from asynchronous code like promises or callbacks.

beginner

What happens if an error occurs inside the try block?

If an error happens inside the try block, the code stops running there and jumps to the catch block where you can handle the error safely.

beginner

Show a simple example of try-catch in Node.js to handle a synchronous error.

try {
  const result = JSON.parse('invalid json');
} catch (error) {
  console.log('Caught an error:', error.message);
}

intermediate

Why can't try-catch catch errors from asynchronous code like setTimeout or promises?

Because asynchronous code runs later, outside the current try-catch block's scope. Errors happen after the try-catch has finished, so they need special handling like .catch() or async/await with try-catch.

What does a try-catch block catch in Node.js?

A No errors

B Synchronous errors

C Both synchronous and asynchronous errors

D Asynchronous errors

Try-catch blocks only catch synchronous errors that happen immediately in the code inside the try block.

Where does the program jump when an error occurs inside a try block?

A To the catch block

B To the next line after try-catch

C To the finally block

D It crashes immediately

When an error occurs, the program jumps to the catch block to handle the error.

Which of these errors will NOT be caught by try-catch?

A Error thrown by JSON.parse with invalid input

B Error thrown inside the try block

C Error thrown inside a setTimeout callback

D Error thrown by a function called inside try

Errors in asynchronous callbacks like setTimeout happen later and are not caught by the surrounding try-catch.

What is the correct syntax to catch errors in synchronous code?

A catch { /* handle error */ } try { /* code */ }

B try { /* code */ } then { /* handle error */ }

C try { /* code */ } finally { /* handle error */ }

D try { /* code */ } catch (error) { /* handle error */ }

The try-catch syntax requires try first, then catch with an error parameter.

If you want to handle errors from a promise, what should you use instead of try-catch?

A .catch() method or async/await with try-catch

B Another try-catch block

C setTimeout

D console.log

Promises handle errors with .catch() or async/await combined with try-catch for asynchronous error handling.

Explain how try-catch works for synchronous errors in Node.js and why it cannot catch asynchronous errors.

Think about when the error happens in relation to the try-catch block.

Write a simple Node.js code example using try-catch to handle a synchronous error from JSON parsing.

Use JSON.parse with a wrong string inside try.