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. However, improper usage 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

One of the most frequent mistakes is neglecting error handling. Async functions can throw errors, and if not caught, they can silently fail.

async function fetchData() {
  const response = await fetch('/data');
  return response.json();
}

fetchData().then(data => console.log(data)); //Error handling missing!

Solution: Always use try...catch blocks to handle potential errors.

async function fetchData() {
  try {
    const response = await fetch('/data');
    return response.json();
  } catch (error) {
    console.error('Error fetching data:', error);
    return null; // or throw error; depending on your error handling strategy
  }
}

2. Overusing Async/Await

While async/await makes asynchronous code look synchronous, it’s not always necessary. Using it unnecessarily can add complexity.

Solution: Use async/await only when dealing with actual asynchronous operations like network requests or timers. For simple synchronous operations, stick to regular functions.

3. Nesting Async/Await Calls

Deeply nested await calls lead to the infamous “callback hell” problem, but in an async/await guise. This makes code difficult to read and maintain.

Solution: Use Promise.all for parallel operations or refactor using helper functions to improve readability.

//Bad
async function nestedCalls() {
  const data1 = await fetchData1();
  const data2 = await fetchData2(data1);
  const data3 = await fetchData3(data2);
  return data3;
}

//Good
async function parallelCalls() {
  const [data1, data2, data3] = await Promise.all([
    fetchData1(),
    fetchData2(),
    fetchData3()
  ]);
  return data3; // Or use all three data points appropriately
}

4. Forgetting to Return Promises

If an async function doesn’t explicitly return a promise, its behavior becomes unpredictable.

Solution: Always ensure that async functions return a promise, either implicitly by using await or explicitly with Promise.resolve().

5. Improper Use of await in Event Handlers

Using await inside event handlers can block the event loop, causing UI freezes or unexpected behavior.

Solution: Handle asynchronous operations within the event handler without await. Use .then() or a separate asynchronous function called from the event handler.

6. Ignoring Promise Rejections

Similar to ignoring errors, ignoring rejected promises leads to silent failures. Use .catch() to handle rejections appropriately.

7. Mixing async/await with callbacks

Mixing async/await with traditional callbacks creates unnecessary complexity and can obscure the asynchronous flow.

Solution: Favor a consistent approach; either use async/await throughout or stick with callbacks.

8. Incorrectly handling timeouts

Timeouts are essential for preventing indefinite waits. Improper handling can lead to deadlocks or unhandled exceptions.

Solution: Use setTimeout and clearTimeout appropriately, ensuring cancellation where necessary. Combine with Promise.race for timeout functionality.

9. Unnecessary Use of async Keyword

Using async when it’s not required adds unnecessary overhead. Use it only on functions that need to perform asynchronous operations.

10. Lack of Testing

Thorough testing is crucial for ensuring the correctness of asynchronous code. Neglecting this can lead to subtle bugs that are difficult to reproduce.

Solution: Implement unit and integration tests using frameworks like Jest or Mocha to verify your async/await functionality.

Conclusion

Async/await offers a cleaner way to manage asynchronous operations in JavaScript. By avoiding these common anti-patterns and following best practices, you can write more robust, maintainable, and efficient asynchronous code.