Async/await error handling patterns in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of using try/catch with async/await in Node.js?

To catch and handle errors that occur during asynchronous operations, preventing the program from crashing and allowing graceful error management.

beginner

How does the 'await' keyword affect error handling in asynchronous functions?

The 'await' keyword pauses the function until the Promise resolves or rejects. If it rejects, the error can be caught by a surrounding try/catch block.

intermediate

What is an alternative to try/catch for handling errors with async/await?

Using Promise methods like .catch() after the awaited function call or wrapping the awaited call in a helper function that returns an error and result tuple.

intermediate

Explain the pattern of using a helper function to handle async errors without try/catch.

A helper function wraps a Promise and returns an array like [error, result]. This lets you destructure the result and error without try/catch, simplifying error checks.

beginner

Why is it important to handle errors in async functions in Node.js?

Because unhandled errors can crash the Node.js process, handling errors ensures the app stays stable and can respond properly to failures.

What happens if an awaited Promise rejects and there is no try/catch?

A The error is silently ignored

B The function returns undefined

C The Promise automatically retries

D The Node.js process crashes or the error is unhandled

Without try/catch, a rejected Promise causes an unhandled rejection, which can crash the Node.js process or cause warnings.

Which pattern helps avoid try/catch blocks by returning [error, result]?

A Promise.all()

B Helper function wrapping Promises

C Callback functions

D Event emitters

A helper function can wrap a Promise and return an array with error and result, allowing error handling without try/catch.

Where should you place try/catch blocks when using async/await?

A Around each awaited call that might fail

B Only outside the main function

C Only in synchronous code

D Never, async/await handles errors automatically

Try/catch should wrap awaited calls that might reject to catch errors properly.

What is the benefit of using async/await over .then()/.catch() for error handling?

A Async/await runs faster

B Async/await automatically fixes errors

C Async/await makes code look synchronous and easier to read

D Async/await disables errors

Async/await syntax makes asynchronous code easier to read and write, improving error handling clarity.

How can you handle multiple async errors simultaneously?

A Use Promise.allSettled() and check results

B Use a single try/catch for all Promises

C Ignore errors in parallel calls

D Use synchronous loops

Promise.allSettled() lets you wait for all Promises and see which succeeded or failed, enabling handling multiple errors.

Describe how to use try/catch blocks with async/await to handle errors in Node.js.

Think about how synchronous try/catch works and apply it to async functions.

Explain the helper function pattern that returns [error, result] for async error handling.

Consider how to handle errors without try/catch by returning both error and data.

Practice

1. What is the main purpose of using try/catch blocks with async/await in Node.js?

easy

A. To handle errors that occur during asynchronous operations

B. To make the code run faster

C. To avoid using promises

D. To automatically retry failed operations

Solution

1. Step 1: Understand async/await behavior

   Async/await pauses code execution until a promise settles, but errors can still happen.

2. Step 2: Role of try/catch

   Try/catch blocks catch errors thrown inside async functions to prevent crashes.

3. Final Answer:

   To handle errors that occur during asynchronous operations -> Option A

4. Quick Check:

   Error handling = D [OK]

Hint: Use try/catch to catch async errors safely [OK]

Common Mistakes:

• Thinking try/catch makes code faster
• Believing async/await removes need for error handling
• Assuming errors auto-retry without code

2. Which of the following is the correct syntax to catch errors in an async function using async/await?

easy

A. async function fetchData() { await fetch(); } catch (e) { console.error(e); }

B. async function fetchData() { (await fetch()).catch(e => console.error(e)); }

C. async function fetchData() { try { await fetch(); } catch (e) { console.error(e); } }

D. async function fetchData() { try await fetch(); catch (e) { console.error(e); } }

Solution

1. Step 1: Identify proper try/catch block usage

   Try/catch must wrap the await expression inside the async function body.

2. Step 2: Check syntax correctness

   async function fetchData() { try { await fetch(); } catch (e) { console.error(e); } } correctly places try before await and catch after the block.

3. Final Answer:

   async function fetchData() { try { await fetch(); } catch (e) { console.error(e); } } -> Option C

4. Quick Check:

   Correct try/catch syntax = C [OK]

Hint: Wrap await inside try block, catch errors after [OK]

Common Mistakes:

• Placing catch outside function body
• Using .catch() on await directly
• Using try without braces

3. What will be logged to the console when running this code?

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

medium

A. fail

B. Caught: fail

C. Uncaught (in promise) fail

D. No output

Solution

1. Step 1: Understand Promise.reject inside try block

   The rejected promise throws an error caught by the catch block.

2. Step 2: Check console.log output

   The catch block logs 'Caught:' followed by the error message 'fail'.

3. Final Answer:

   Caught: fail -> Option B

4. Quick Check:

   Error caught and logged = B [OK]

Hint: Rejected promises inside try are caught by catch [OK]

Common Mistakes:

• Expecting unhandled rejection error
• Thinking error is logged without 'Caught:' prefix
• Assuming no output because of rejection

4. Identify the error in this async function error handling code:

async function load() {
  try {
    const data = await fetchData();
  } catch {
    console.error(error);
  }
}

medium

A. console.error cannot log variables

B. Await cannot be used inside try block

C. fetchData() must be awaited outside try

D. Missing error parameter in catch block

Solution

1. Step 1: Check catch block syntax

   The catch block is missing the error parameter to receive the thrown error.

2. Step 2: Understand console.error usage

   console.error(error) references a variable 'error' which is undefined without catch parameter.

3. Final Answer:

   Missing error parameter in catch block -> Option D

4. Quick Check:

   Catch needs error param = A [OK]

Hint: Always name error in catch(e) to use it inside [OK]

Common Mistakes:

• Omitting error parameter in catch
• Misplacing await outside try
• Misusing console.error syntax

5. You want to run multiple async tasks in parallel and handle errors individually without stopping all tasks. Which pattern correctly handles errors for each async call using async/await?

hard

A. Wrap each await call inside its own try/catch block

B. Use Promise.all with a single try/catch around it

C. Use await inside a forEach loop with one try/catch outside

D. Ignore errors and rely on process.on('unhandledRejection')

Solution

1. Step 1: Understand parallel async calls and error handling

   Promise.all stops on first rejection; one try/catch around it catches all or none.

2. Step 2: Individual error handling requires separate try/catch

   Wrapping each await in its own try/catch lets errors be handled separately without stopping others.

3. Final Answer:

   Wrap each await call inside its own try/catch block -> Option A

4. Quick Check:

   Individual error handling = A [OK]

Hint: Try/catch each await separately for independent error handling [OK]

Common Mistakes:

• Using Promise.all with one try/catch stops all on first error
• Using forEach with await causes unexpected behavior
• Ignoring errors leads to crashes or silent failures