Question 1

What is the practical difference between using async/await and dealing directly with promises in Node.js?

Accepted Answer

async/await is just syntactic sugar built on top of promises that makes code look like synchronous code, allows error handling with try/catch, and improves the readability of stack traces.

Question 2

Compare Promise.all, Promise.allSettled, and Promise.race in Node.js in terms of behavior and error handling.

Accepted Answer

Promise.all fails as soon as any promise is rejected, Promise.allSettled waits for all to complete in success and failure, while Promise.race settles its result with the first promise to finish whatever its state.

Question 3

Why is running hundreds of promises through Promise.all dangerous and how do you apply concurrency limiting?

Accepted Answer

Running a huge number in parallel drains network ports, file handles, and server memory, and concurrency must be restricted with a limiter (a pool or semaphore).

Question 4

What is the AsyncLocalStorage technique in Node.js and what problems does it solve in request tracing?

Accepted Answer

It provides a local context store that lets you share request data (such as the request ID and user) across all asynchronous operations without passing it manually.

Question 5

How does the priority of microtasks differ from macrotasks in task processing in Node.js?

Accepted Answer

Microtasks run as soon as the current task ends and before any later macrotask, which means the microtask queue is drained completely before advancing through the event loop phases.

Question 6

How do errors travel in asynchronous code and what is the danger of errors inside traditional callbacks?

Accepted Answer

Promise errors travel through rejection chains, while outer try/catch blocks fail to catch errors inside traditional callbacks, causing the server to crash.

Question 7

What is the event loop starvation phenomenon caused by CPU-intensive tasks and how do you avoid it?

Accepted Answer

It happens when a long synchronous computation monopolizes the main thread, preventing I/O and timers from being processed, and it can be avoided by chunking the computation or delegating it to worker threads.

Question 8

What is the top-level await feature in ES modules in Node.js and what are the cautions of using it?

Accepted Answer

It lets you use await directly at the top level of the file without wrapping it in an async function, and its caution is that it can delay loading dependencies or freeze the app's startup.

Question 9

How do async iterators and the for await...of loop help consume data streams in Node.js?

Accepted Answer

They provide a unified API for consuming streamed data item by item or batch by batch, with automatic backpressure and pausing the fetch until the consumption of the item finishes.

Question 10

What is the concept of async disposable resources and the Symbol.asyncDispose symbol?

Accepted Answer

A pattern for managing and cleaning up resources automatically (such as network connections and files) when leaving the scope through the await using keyword.