How do you read a file asynchronously in Node.js?

0-2 years experience

1. 1We need to read a JSON config file at startup without blocking the event loop. How would you implement that using Node's async APIs?
2. 2If you use fs.readFile with a callback and the file doesn't exist, what will happen and how would you handle the error?
3. 3Can you write a short snippet that reads a text file asynchronously and logs its contents?

2-5 years experience

1. 1Our service reads user‑uploaded CSV files and processes them line by line. Why might using fs.readFile be problematic, and how would you change the implementation?
2. 2During a recent deployment, the async file read started throwing 'EMFILE' errors under load. What does that error mean and how would you mitigate it?
3. 3We switched from callbacks to fs.promises.readFile. What are the benefits and any gotchas you need to watch for in existing code?

5-8 years experience

1. 1Design a file‑reading utility that can safely handle thousands of concurrent reads in a high‑traffic API. What patterns or Node features would you use to avoid resource exhaustion?
2. 2Explain how you would implement back‑pressure handling when streaming large files to a client, ensuring the server stays responsive.
3. 3If we need to read files from a network‑mounted drive with variable latency, how would you structure the async reads to maintain overall request latency targets?

8+ years experience

1. 1Our monolith is being broken into microservices, and many services need to read shared configuration files. How would you redesign the async file‑reading approach to support consistency, caching, and deployment flexibility across teams?
2. 2We are considering moving from Node's built‑in fs module to a custom abstraction that can read from both local disk and cloud storage. What architectural considerations and trade‑offs should guide that design?
3. 3Discuss the long‑term maintenance implications of using callbacks vs promises vs async/await for file I/O across a large codebase, and how you would drive a migration strategy.