JavaScript’s Top 10 Async/Await Anti-Patterns (and How to Avoid Them)

Async/await is a powerful feature in JavaScript that simplifies asynchronous code, making it more readable and maintainable. However, misuse can lead to unexpected behavior and difficult-to-debug issues. This post outlines ten common async/await anti-patterns and provides solutions to avoid them.

1. Ignoring Errors

Async functions can throw errors just like synchronous functions. Failing to handle these errors can lead to silent failures and unexpected application behavior.

async function fetchData() {
  try {
    const response = await fetch('some-url');
    const data = await response.json();
    // Process data
  } catch (error) {
    console.error('Error fetching data:', error);
    // Handle the error appropriately, e.g., display a message to the user
  }
}

2. Overusing Async/Await in Synchronous Code

Using async/await unnecessarily in purely synchronous functions adds complexity without benefit.

//Avoid this:
async function add(a, b) {
  return a + b;
}

// Prefer this:
function add(a, b) {
  return a + b;
}

3. Nested Async/Await Calls (Pyramid of Doom)

Deeply nested async/await calls create difficult-to-read and maintain code. Use techniques like Promise.all or refactoring to handle multiple asynchronous operations concurrently or in a more manageable way.

//Avoid this (Pyramid of Doom):
async function fetchData() {
  const data1 = await fetch('url1');
  const data2 = await fetch(await data1.json().then(data => data.nextUrl));
  const data3 = await fetch(data2);
}

//Prefer this (using Promise.all):
async function fetchData() {
  const [data1, data2, data3] = await Promise.all([
    fetch('url1'),
    fetch('url2'),
    fetch('url3')
  ]);
}

4. Forgetting await

Forgetting await before a promise will result in the function not waiting for the promise to resolve, leading to race conditions and unexpected results.

// Incorrect:  The fetch call isn't awaited
async function fetchData() {
  const response = fetch('some-url'); // Missing await
  const data = await response.json(); // This will likely fail
}

5. Mixing Async/Await with Callbacks

Mixing async/await with callbacks leads to less readable and maintainable code. Prefer to keep your code consistent.

6. Unhandled Rejections

Unhandled promise rejections can lead to application crashes or unexpected behavior. Use .catch() blocks to handle potential errors in asynchronous operations.

7. Incorrect Error Handling in Promise Chains

Improperly handling errors in a chain of promises using .then() and .catch() can lead to missed errors. Async/await makes error handling more straightforward.

8. Blocking the Event Loop

Long-running operations within an async function can block the event loop. For CPU-intensive tasks, consider using Web Workers.

9. Ignoring finally Blocks

A finally block in a try...catch statement ensures cleanup actions (like closing connections) are always executed, regardless of success or failure.

10. Overcomplicating Simple Tasks

Avoid using async/await for tasks that don’t require asynchronous operations. Synchronous functions are often simpler and more efficient for simple tasks.

Conclusion

Async/await is a powerful tool, but its misuse can introduce subtle bugs that are difficult to track down. By understanding and avoiding these common anti-patterns, you can write cleaner, more maintainable, and less error-prone asynchronous JavaScript code.