Async/await error handling patterns in Node.js - Performance & Optimization

Performance: Async/await error handling patterns

MEDIUM IMPACT

This affects how asynchronous errors impact event loop responsiveness and error propagation speed in Node.js applications.

Handling errors in asynchronous functions using async/await

Node.js

async function fetchData() {
  try {
    const data = await fetch('https://api.example.com/data');
    const json = await data.json();
    return json;
  } catch (error) {
    console.error('Fetch failed:', error);
    throw error; // propagate error properly
  }
}

fetchData().then(console.log).catch(console.error);

Catching errors inside async function avoids unhandled rejections and allows immediate error handling, keeping event loop responsive.

📈 Performance GainPrevents event loop blocking from unhandled errors, improving INP and reducing error propagation delays.

Handling errors in asynchronous functions using async/await

Node.js

async function fetchData() {
  const data = await fetch('https://api.example.com/data');
  const json = await data.json();
  return json;
}

fetchData().then(console.log).catch(console.error);

Errors inside async function are only caught at the call site, which can lead to unhandled promise rejections if .catch is missed.

📉 Performance CostUncaught errors can cause unhandled promise rejections, potentially blocking event loop for error handling and degrading INP.

Performance Comparison

Pattern	Event Loop Blocking	Error Handling Speed	Parallelism	Verdict
Sequential awaits without try/catch	High (multiple awaits block event loop)	Slow (errors caught late)	No	[X] Bad
Try/catch inside async function	Low (errors caught immediately)	Fast (immediate error handling)	No	[OK] Good
Sequential awaits in loop with try/catch	High (multiple awaits block event loop)	Moderate	No	[!] OK
Parallel async calls with Promise.all and try/catch	Low (single event loop wait)	Fast (errors caught early)	Yes	[OK] Good

Rendering Pipeline

Async/await error handling affects the Node.js event loop and microtask queue, influencing how quickly errors are caught and handled without blocking other tasks.

→Event Loop

→Microtask Queue

→Error Propagation

⚠️ BottleneckEvent Loop blocking due to unhandled or delayed error handling

Core Web Vital Affected

INP

This affects how asynchronous errors impact event loop responsiveness and error propagation speed in Node.js applications.

Optimization Tips

1Always use try/catch inside async functions to catch errors early.

2Avoid sequential awaits in loops; use Promise.all for parallelism.

3Proper error handling prevents event loop blocking and improves responsiveness.

Performance Quiz - 3 Questions

What is the main performance benefit of using try/catch inside async functions with await?

A It makes the code run synchronously for faster execution.

B It reduces bundle size by removing error handling code.

C It catches errors immediately, preventing event loop blocking.

D It delays error handling to batch process errors later.

DevTools: Performance

How to check: Record a performance profile while running your Node.js async code. Look for long tasks blocking the event loop and check the microtask queue timing.

What to look for: Look for long blocking periods caused by sequential awaits and delayed error handling. Faster error handling shows shorter blocking and quicker microtask resolution.

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