JavaScript’s Top 10 Async/Await Gotchas (and How to Avoid Them)

Async/await makes asynchronous JavaScript code look and feel a lot like synchronous code, which is a huge win for readability and maintainability. However, this syntactic sugar can mask some subtle pitfalls. Let’s explore ten common gotchas and how to avoid them.

1. Unhandled Promise Rejections

Even with async/await, unhandled promise rejections can silently crash your application. Always handle potential errors with try...catch blocks.

async function myFunc() {
  try {
    const result = await somePromiseThatMightReject();
    // ...
  } catch (error) {
    console.error('Error:', error);
    // Handle the error appropriately
  }
}

2. Forgetting await

Using await only works inside an async function. If you forget await before a promise, the code will continue executing without waiting for the promise to resolve, leading to unexpected results.

// Incorrect - will not wait
async function incorrectFunc() {
  const result = somePromise(); // Missing await
  console.log(result); // result might not be resolved yet
}

// Correct - waits for the promise
async function correctFunc() {
  const result = await somePromise();
  console.log(result); // result will be resolved
}

3. Nested try...catch Blocks

While sometimes necessary, deeply nested try...catch blocks can become difficult to read and maintain. Consider refactoring to improve clarity.

4. await in a non-async function

This will result in a SyntaxError. Always use await inside an async function.

5. Incorrect Error Handling in Promises

Ensure that your promises handle errors properly, even if you use async/await to consume them. A rejected promise will still need to be caught.

6. Mixing async/await with callbacks

While possible, mixing callbacks with async/await can lead to confusing code. Try to maintain consistency in your approach.

7. Overuse of async/await

Not every asynchronous operation requires async/await. For simple cases, .then() and .catch() might be more concise.

8. Ignoring await return values

If the awaited promise resolves with a value, make sure to use it. Otherwise, you are losing valuable data.

9. Deadlocks (in concurrent code)

With async/await and concurrent operations, be careful to avoid creating deadlocks. This typically involves multiple asynchronous operations waiting on each other.

10. Debugging Challenges

Debugging asynchronous code can be more difficult than debugging synchronous code. Use debugging tools effectively, setting breakpoints and stepping through the code line by line. Console logging can also help track the flow of execution and identify problematic areas.

Conclusion

Async/await significantly improves the readability of asynchronous JavaScript, but it is crucial to understand its potential pitfalls. By being mindful of these common gotchas and following best practices, you can write robust and maintainable asynchronous code.