Error handling with async and await in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of async function with try-catch

What will be the output of this code when run in a modern JavaScript environment?

Javascript

async function test() {
  try {
    await Promise.reject('fail');
  } catch (e) {
    console.log('Caught:', e);
  }
}
test();

A undefined

B Caught: fail

C Uncaught (in promise) fail

D SyntaxError

💡 Hint

Remember that await inside try-catch can catch rejected promises.

The rejected promise is caught by the catch block, so the console logs 'Caught: fail'.

❓ Predict Output

intermediate

Error propagation in async functions

What will be logged to the console when this code runs?

Javascript

async function foo() {
  throw new Error('Oops');
}

foo().catch(e => console.log(e.message));

A Oops

B undefined

C Uncaught Error: Oops

D Error: Oops

💡 Hint

Check how the catch method on the promise handles the error.

The error thrown inside async function foo is caught by the catch method, logging only the message 'Oops'.

❓ Predict Output

advanced

Handling multiple awaits with error catching

What will be the output of this code snippet?

Javascript

async function process() {
  try {
    await Promise.resolve('First');
    await Promise.reject('Second');
    console.log('Done');
  } catch (err) {
    console.log('Error:', err);
  }
}
process();

A Error: Second

B Done

C Error: First

D Uncaught (in promise) Second

💡 Hint

The first await resolves, the second rejects and triggers catch.

The first await resolves successfully, but the second await rejects, so the catch block logs 'Error: Second'.

❓ Predict Output

advanced

Effect of missing await on error handling

What will be the output of this code?

Javascript

async function run() {
  try {
    Promise.reject('Fail');
  } catch (e) {
    console.log('Caught:', e);
  }
}
run();

A Caught: Fail

B undefined

C Uncaught (in promise) Fail

D SyntaxError

💡 Hint

Without await, the rejection is not caught by try-catch.

The Promise.reject creates a rejected promise, but without await, the try-catch does not catch it, causing an unhandled rejection.

🧠 Conceptual

expert

Why use try-catch with async/await?

Which statement best explains why try-catch blocks are used with async/await in JavaScript?

A To prevent the event loop from blocking

B To make asynchronous code run faster

C To convert promises into callbacks

D To handle errors from rejected promises in a synchronous-looking way

💡 Hint

Think about how async/await changes the way we write asynchronous code.

Try-catch blocks allow handling errors from promises as if the code was synchronous, making it easier to read and maintain.