Async/await best practices?

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Riya Sharma Author
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1 day ago Asked
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Hey everyone, I'm currently refactoring some older JavaScript code in our SaaS backend and trying to modernize it with async/await. I'm looking for any best practices or common pitfalls to watch out for, especially regarding performance and stability when dealing with numerous promises. Any seasoned JavaScript developers have insights on optimizing async/await usage? Really keen to hear your advice.

javascript async/await Performance webdev

1 Answers

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Zuri Diallo
Answered 13 hours ago
  • Error Handling: Always wrap your `await` calls in `try...catch` blocks. Unhandled promise rejections can crash Node.js processes, especially in a backend environment. For scenarios where you're awaiting multiple independent promises, consider using `Promise.allSettled()` instead of `Promise.all()`. While `Promise.all()` fails fast if any promise rejects, `Promise.allSettled()` waits for all promises to resolve or reject, providing an array of objects describing the outcome of each promise, which is invaluable for robust error reporting and partial success scenarios.
  • Parallel Execution (Concurrency): Avoid sequential `await` calls when operations are independent. For example, instead of: 
    const result1 = await fetchData1();
const result2 = await fetchData2();
const result3 = await fetchData3();
    Execute them in parallel using `Promise.all()`: 
    const [result1, result2, result3] = await Promise.all([
    fetchData1(),
    fetchData2(),
    fetchData3()
]);
    This significantly improves performance by allowing the JavaScript runtime to execute these asynchronous operations concurrently rather than waiting for each to complete before starting the next.
  • Limit Concurrency for Resource-Intensive Tasks: When dealing with a large number of promises, such as making many API calls or database writes, directly using `Promise.all()` can overwhelm system resources or hit rate limits. Implement a mechanism for `concurrency control` to process promises in batches. Libraries like `p-queue` or `bottleneck` can help manage a limited number of concurrent operations, preventing resource exhaustion and improving stability.
  • Avoid `async` in Loops Unless Necessary: While sometimes unavoidable, repeatedly `await`ing inside a `forEach` or `for...of` loop will process each iteration sequentially. If the operations in the loop are independent, collect all promises into an array and then use `Promise.all()` outside the loop. 
    // Bad (sequential)
for (const item of items) {
    await processItem(item);
}

// Good (parallel)
const promises = items.map(item => processItem(item));
await Promise.all(promises);
  • Return Promises Directly: If an `async` function's only purpose is to `await` another promise and return its result, you can often simplify it by just returning the promise directly. This avoids unnecessary `async` overhead. 
    // Less efficient
async function getData() {
    return await fetch('/api/data');
}

// More efficient
function getData() {
    return fetch('/api/data');
}
  • Consider Cancellation: For long-running operations in a SaaS backend, especially user-initiated ones, the ability to cancel pending promises can improve resource management. While JavaScript Promises don't have built-in cancellation, you can implement it using patterns like `AbortController` (for Fetch API) or by wrapping promises with a cancellable wrapper. This prevents unnecessary work if a user navigates away or an operation becomes irrelevant.

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