Async/await error handling patterns in Node.js - Mini Project: Build & Apply

Async/Await Error Handling Patterns in Node.js

📖 Scenario: You are building a simple Node.js app that fetches user data from a mock API. You want to handle errors properly using async/await patterns.

🎯 Goal: Learn how to write async functions with proper error handling using try/catch blocks and helper functions.

📋 What You'll Learn

Create an async function that fetches user data

Add a configuration variable for the API URL

Use try/catch inside the async function to handle errors

Add a helper function to wrap async calls and handle errors gracefully

💡 Why This Matters

🌍 Real World

Handling errors in async functions is essential for building reliable Node.js applications that interact with APIs or databases.

💼 Career

Understanding async/await error handling patterns is a key skill for backend developers working with Node.js to write clean, maintainable, and robust code.

1

Create the async function to fetch user data

Create an async function called fetchUserData that takes a parameter userId and returns a resolved Promise with the string `User data for ${userId}`.

Node.js

// Your code here

Hint

Use the async keyword before the function and return a template string with the userId.

2

Add the API URL configuration variable

Add a constant variable called API_URL and set it to the string 'https://api.example.com/users'.

Node.js

async function fetchUserData(userId) {
    return `User data for ${userId}`;
}

// Your code here

Hint

Use const to declare API_URL with the exact string value.

3

Add try/catch error handling inside the async function

Modify the fetchUserData function to include a try/catch block. Inside try, return the string `User data for ${userId}`. In catch, throw a new Error with the message 'Failed to fetch user data'.

Node.js

async function fetchUserData(userId) {
    // Add try/catch block here
    // Your code here
}

const API_URL = 'https://api.example.com/users';

Hint

Wrap the return statement inside try and handle errors in catch by throwing a new Error.

4

Create a helper function to handle async errors

Create an async function called handleAsync that takes a parameter asyncFunc. Inside, use try/catch to await asyncFunc(). Return an object with { data } if successful or { error } if an error occurs.

Node.js

async function fetchUserData(userId) {
    try {
        return `User data for ${userId}`;
    } catch (error) {
        throw new Error('Failed to fetch user data');
    }
}

const API_URL = 'https://api.example.com/users';

// Your code here

Hint

Use try/catch inside handleAsync to await the function and return an object with either data or error.

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