Async/await error handling patterns in Node.js

Introduction

Async/await helps write code that waits for tasks to finish. Handling errors properly keeps your program safe and clear.

When calling a function that returns a promise and might fail

When you want to catch errors from asynchronous operations cleanly

When you want to avoid nested callbacks and make code easier to read

When you need to handle multiple async tasks and catch their errors

When debugging async code and want clear error messages

Syntax

Node.js

try {
  const result = await asyncFunction();
  // use result
} catch (error) {
  // handle error
}

Use try to run code that might fail.

Use catch to handle any errors from the await call.

Examples

This example fetches data from an API and catches any errors during the fetch or JSON parsing.

Node.js

async function fetchData() {
  try {
    const data = await fetch('https://api.example.com/data');
    const json = await data.json();
    console.log(json);
  } catch (error) {
    console.error('Error fetching data:', error);
  }
}

This example reads a file asynchronously and handles errors if the file is missing or unreadable.

Node.js

import fs from 'fs/promises';

async function readFile() {
  try {
    const content = await fs.readFile('file.txt', 'utf-8');
    console.log(content);
  } catch (error) {
    console.error('Failed to read file:', error);
  }
}

This example runs two async tasks in sequence and catches errors from either.

Node.js

async function processTasks() {
  try {
    const result1 = await task1();
    const result2 = await task2();
    console.log(result1, result2);
  } catch (error) {
    console.error('One of the tasks failed:', error);
  }
}

Sample Program

This program tries to read a JSON config file asynchronously. If the file is missing or contains invalid JSON, it catches the error and prints a clear message.

Node.js

import fs from 'fs/promises';

async function readConfig() {
  try {
    const data = await fs.readFile('config.json', 'utf-8');
    const config = JSON.parse(data);
    console.log('Config loaded:', config);
  } catch (error) {
    console.error('Error loading config:', error.message);
  }
}

readConfig();

Important Notes

Always use try/catch around await to avoid unhandled promise rejections.

You can also use Promise.allSettled() for multiple async calls to handle errors individually.

Logging error messages helps find problems quickly.

Summary

Use try/catch blocks to handle errors with async/await.

This makes async code easier to read and safer.

Always catch errors to prevent your program from crashing unexpectedly.

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